Whats the difference between a barefoot trim and regular trim?

I know this sounds horrible, but when my [certified] farrier comes to do my mare's and my friend's gelding's hooves he just asks "what do you want?" and we say either a trim or reset the shoes. I haven't put shoes on her and just ask for a trim. I plan on riding her on trails in the summer and doing groundwork, lunging and work in the arena. Anyways, what's the difference?