I was spanked as a child. Got grounded for over a year once (sadly it was probably earned, I'd rather not go into details XD ), and so on.
To be brutally honest though, I know I wouldn't've been nearly as well adjusted as I became without it either. It sucked at the time, and instilled a great deal of pure fear... but it worked. I really don't think I had much in the way of true reasoning capacity until I was about 12-14 or so, when it seemed to start showing up, I could 'think' but not in nearly the same fashion I do now. The idea of thinking things out long term and anticipating how things would react was pretty much 100% beyond me, I lived in the moment with no thought for whot would happen until after the fact. Drop in a short attention span and poor memory, and I'd often make the same mistakes repeatedly.
Adding a sense of physical fear helped the memory latch onto things that were BAD, and slowly conditioned towards actually trying to avoid it in the first place, encouraging more actual forethought in the process.
This's eventually evolved over time into the fact that I now try to avoid ever repeating a mistake I've made, and attempt to learn from other's mistakes so I don't suffer the same fate of wasted time, energy, and possible other unfortunate complications as well.
This brings me to the problem I have with the "zomg don't spank kids >=O " the concept is great... in theory. But the theory relies heavily upon flawed assumptions, primarily that children process information in exactly the same way adults do. Very often they don't understand things the way we do in the slightest... and trying to explain that the stove is hot and dangerous can be painfully difficult to do, or to not play in the street. Having an element of fear that they RECOGNIZE can get the message across much faster. Saying yeu "might get hurt or killed" by playing in the road isn't something that all children will neccesarily believe or take to heart... saying "I'm going to spank yeu if I see yeu out there one more time >=O " and showing obvious anger over their action can instill enough DIRECT fear of doing so that they won't do it anymore. Indirect fear often just doesn't have nearly the same effect as they may not understand it in the same way. Sure, these days I may be horrified at the idea of disappointing someone I hold great respect for, but when I was say... 6? Pft if I got grounded to my room for a week it was far preferable to getting spanked, even if it was a much longer duration. Common sense NOW says that a short displeasure would be better than a long one, but I didn't think that way back then at all.
It depends on how the child thinks and reacts though, if they don't seem capable of grasping explaining things carefully, then fear may be the next best option, as it has an immediate and lasting effect, and can be far more readily understood even at an early age.
There's alot of parents who won't even attempt to discipline their children in any way... I think we've all seen the brat in the store screaming at one point or another, while the parent just stands by and asks them politely to stop, treating them as if they were an adult and thinking reason works just fine with them. It doesn't always work... some children it WILL work on, and for those situations it's great! The ones where it doesn't... well there's a simple quote that works quite well, being that only an idiot would keep performing the same action repeatedly, and expect a different reaction every time. If it doesn't work, yeu may be required to resort to force, as much as yeu may not want to. If it's the only way to get the message across, then it has to be done.
Obviously I'm not saying to jump right at the whole spanking first thing, but once yeu've exhausted other alternatives, then don't be scared to. It *CAN* be taken to abusive levels (practically whipping in some cases...) at times, but it doesn't mean that by default it's especially abusive. Of course, on adults it would be by default, since they can think for themselves, and beating them doesn't teach them anything that yeu couldn't teach with discussion.
The problem is that children are NOT adults, they are not just "little versions of ourselves". They think quite differently, and act differently. They don't have the same inhibitions, nor the same fears, or level of understanding. If I were to run down the middle of the street in the nude, the police would be after me in no time. (please don't imagine that XD ) but a little kid may often do so without even a second thought, especially on a hot summer day if there's sprinklers out in the yards. Obviously the mindset's different, and the capacity to understand social rules is not the same at all.
But once again, I stress not to jump to spanking as the first thing to do every time... it has its' uses as a tool, but it has alot of risks associated with it as well. It does work well as a last ditch effort for a child who won't see reason otherwise. They're not reasonable creatures for the most part, despite that they do have the capacity for a degree of reason, it's just not nearly on the same level until later in life. Brain development plays a major role.
Obviously, spanking a teenager really just doesn't work the same way as it does a 5 year old, as they view things significantly differently. The message would seriously not get across at all. So at some point, the need for it, even in exceptional cases, will be diminished to the point of disuse, in favour of other forms of 'behavioural encouragement'.
The best option is to provide both a positive and negative reinforcement at the same time; punish when something's done wrong, provide rewards for when things are done right. If it's one sided, it's not nearly as effective. ESPECIALLY if yeu ONLY punish when something's done wrong, and don't provide warning or explaination in advance... then yeu're just stuck with a child who doesn't know whot to expect, they can become withdrawn and scared to do much of anything as punishment appears to be random without consistant application. Of course just heaping on praise and rewards at every opportunity, even if one does something wrong then something right after, need to explain whot it's for and make sure they understand. If they don't know WHY they're in trouble, they'll never learn the lesson. I'd had more than one occasion where I was spanked/grounded/etc for "think about whot yeu've done!" and I honestly DIDN'T KNOW. That just breeds confusion and doesn't do anything useful at all. It has to be clear and obvious cause and effect to make sense, just 'assumming' they know because yeu do as the parent is silly, because yeu have a much better idea of how to process information, and yeu actually KNOW whot upset yeu, they may not, and if yeu leave it to them to guess, they may guess wrong, and still do the same error again without understanding, or they may just start to hate yeu because they have no clue why they keep getting in trouble seemingly at random.
In any case, tools are useful... if used right. Make sure to increase yeur toolset, leading by example, discussion before things become a problem, that kind of thing, are also highly useful. If yeu only have one tool (spanking), then everything will be treated in respect to it (if all yeu have is a hammer, everything looks like a nail).
Of course this topic's waaaay past the original message now, but I don't want to miss my chance to put my two cents in XD