Great question Weber! Often wonder myself. The worries about security, are easily circumvented; just putting in general likes,dislikes, areas of possible expertise, and bits of background info are in no way a security risk. Having that slight idea of personality only aids in giving better answers to the person asking, just as periodically going and seeing how and which Q's and A's the person asks and answers add to that. If total impersonal, pure factual answers are looked for, be better and easier to just Google and search.
I didn't at first, because I didn't even think about it. I went into my profile one day and saw the whole thing was blank. I did eventually fill in some of it, but some of it just doesn't flow for me. There's always more (or less) that I want to say.
I did for a while, but then it started to bug me (a bit) at times. Every once in a while certain questions or answers can get personal and I don't like to put too much of myself out there all at once. I'm sure not many care too much, but if it makes me feel better...then that's what matters the most. What I have on my profile now is personal without being too personal. Every so often I might add a little here and there, but those things usually don't stay on there all the time.