I never used one at all until I built my cabinet. then I didn't have a keyboard and could start them. I also wanted friend to be able to play without me telling them how.
It's also nice to have one front end or gui that can run muliple emulators (mame is GREAT, but for almost every other emulator is better for their games. Mainly because most of the mame drivers are written by people that have created optimized versions in the past).
last, I didn't want my cabinet to look like it was built ontop of windows. I wanted it to 100% have it's own look and feel.