Yep, I get this ultra-concentration at times, too. I can't focus, I can't focus, I can't focus, and then finally, finally I can concentrate enough to get stuff done - I may as well get as much done in these uncommon instances as possible!
The times it usually happens is when I have a deadline and so I have no choice but to focus and work - once I'm focused I can stay focused for hours and hours on end. It's definitely a major plus when it comes to cramming and last-minute work like that, but on the other hand, my time management skills are very poor - all through high school I coped just fine (even more than fine) with last-minute study/homework and nothing more.
However, I'm doing a degree now which involves huge projects - like easily 40+ hours of work each. Which, regardless of one's concentration skills, one simply cannot produce the night before. So it's been a seriously steep learning curve for me, and even now I'm still struggling to work consistently. I'm getting there, but yeah, it's definitely not a natural sort of method for me. So, it's definitely advantageous to have, but we really have to be careful not to completely forget about just concentrating normally!
Example: I had to present a class today (so a 45-minute or so talk), but my thumb drive freaked out and I had to start everything again at around midnight last night... Somehow, I was able to work right through and up to the 8am class, and then present the thing as if I'd practiced it a hundred times. So that was eight hours straight - not counting what I'd worked on before it freaked out, and at the end of it I was as clear and coherent as if I'd had all the sleep in the world. (For the record, though, I did indeed need a nap later in the day. )
But yeah, and I know I've done 12+ hour stints before without much more than a short break.