Re: I was thinking to get in touch with my school mates (after 6 years). Should
When meeting old friends, they will either barely remember you or already have a set image of how you were back then. The former is easier to deal with, I'm sure that's no what you are asking about, but the latter situation leads to cognitive dissonance or incongruity of who you are vs the person you were. This can either work for or against you depending on many factors, but then again, after 6 years things get fuzzy for anyone not part of your main social circle and even then, unless they're genetic freaks, that "set image" is weak and mold-able (obviously, if you were the butt-monkey of the school or the quarterback of the football team, this image is more concrete). Cognitive dissonance works both ways as well, don't be surprised if a few school mates are completely different from how you remember them.
An important note is to
never compare yourself to how you are now vs how you were. It's not really important who you were as long you did the same things they did or knew the same teachers. This makes it harder for the cognitive dissonance to pass and thus for them to view you in your current light. I once made a mistake of calling out my hypocritical asshole-ish behaviour from middle school and had to do damage control. Also remember that others can and will hold grudges if they think you cheated or otherwise hurt them... fun stuff
You said yourself that whenever it is a bad idea or not depends on your goals, and it also depends on their level of contact. I assume you mean high school mates in which case I would not worry about it, but I would consider whenever or not these people work in same or related career fields. If they can be of some use for business on the good end of the spectrum, or get you fired/make life difficult on the bad end; I wouldn't waste time trying to get dat 'tang and do random pickups/clubbing/what-have-you.
If it doesn't affect work now or in the future, go crazy!