Ti-users are constantly scanning for 'true/false' remarks. Because we are independent in our usage of Ti, we constantly are evaluating and re-evaluating the validity of statements. If someone says "sweaters are comfortable" and we have any reason to disagree, we will openly state our opinion, often times without considering Fe-based concerns like, "Is it really worth arguing about?" I think xNTPs are more prone to arguing for the sake of arguing due to their Ne allowing them to evaluate every possible angle and play devil's advocate.
As for Ti in general, we basically just want to make sure everything "makes sense". If things don't seem to line up with the way we understand the world works (which should be a relatively accurate mental model, if the Ti-user is intelligent and healthy), then we MUST question it or re-evaluate our own understanding, because to ignore it is to invite disaster. Take, for instance, if you are being scammed by another person; Ti is the function (maybe a bit of Ni as well, depending) that allows us to notice inconsistencies in what other people say, say to ourselves "Wait, THAT'S not right. Why would they be telling me that?" and then use our other functions to help come up with various reasons explaining the inconsistent behavior.
Note that this process for xxTPs differs depending on dom/aux function. An xNTP would probably come up with many different reasons (Ne) and then hone in on the right one due to a combination of their logic (Ti) and past experience (Si) to re-evaluate every option until they come to as close of a correct conclusion as possible. xSTPs, on the other hand, look at all the details of the situation in front of them (Se) and then infer from those details (Ni) the correct conclusion (or close to correct, in many cases, because xSTPs may not have developed their Ni enough to not jump to some pretty whacked conclusions sometimes-- speaking from experience here.)
So in other words, instead of evaluating whether or not something "feels" right (Fi) based on our own visceral reactions, we instinctively evaluate what "makes sense" (Ti). It should be noted that all types can use Ti/Fi to an extent, but Fi-users will feel alienated by having to strip everything down to logical analysis because it goes against what they normally rely on. Likewise, Ti-users feel alienated by Fi because we ourselves are alienated by instinctively following our "hearts" rather than our "heads". For instance, every time I try to sit down and write song lyrics and/or a very emotional scene, I have a tendency to feel embarrassed with myself or feel like I can't be sincere/serious, so oftentimes I'll end up writing something really narm-y or over-the-top on purpose as a way of undamming the emotional cork.
Some on this forum decry it's value.
