Since folks keep asking me what conventions I work and whether I'm a staff member at such and such convention, I figured it was about time I made a list.
Often this is done on the basis of referrals--if I think a con is interesting/cool, there's a chance I'll know someone who is on staff and inquire through them what the staff experience is like and if it's worth working. If I receive positive answers, I'll inquire about joining staff.
If it's a convention where I don't know any staff (as was the case many many years ago), I'll volunteer first and see how I like it. If I have a positive experience, I'll ask about being on staff in a future year (or asked to be on staff, in a couple of cases).
Many reasons. First, since I am not an artist or a fursuiter, it gives me a chance to make positive contributions to the community. Second, it provides me with a bit of structure to the convention--having to be in certain places at certain times helps me better organize how I spent my time at the con. And finally, it gives me an opportunity to meet people--I've made many many friends over the years just by staffing cons... and getting to see these people again at future cons makes the experience just so much more fun.