I didn't chew gum for years, mostly because my parents thought it was 'dirty' and also threatened that if I swallowed it, it would tie knots in my stomach. I love the way parents tell their kids these sort of outrageous lies!

Anyway, I chew it now because
a) blowing bubbles is fun
b) I like the minty taste but hate the chalkiness of polos and extra-strongs
c) It's good for my teeth.

I’ve seen it suggested that if you chew more as a child (say, with chewing gum) then your mouth grows larger, and you are less likely to have problems with wisdom teeth in later life.

I chew it as a fidget object at work. I often need to fidget in some way or other to stop being distracted, and chewing gum is somewhat more acceptable than chewing coffee stirrers, and it won't make me chubby like proper food.

Exactly. If you've got a brain that will divert need-to-fidget from fingers to mouth, gum is an excellent fiddle object. So are cigarettes for that matter, especially if you roll your own.