Haven't done it but am thinking about trying it on a roadbike. Well I do have a fixed gear but that's a little different.
As I see it the advantages are this: Most riders don't use that many gears and with 8-9 now available at the rear you can simplify your driveline and save a small amount of weight w/o losing anything you don't use anyways. I have bikes with up to 27 "speeds" but seldom use more than 3-4.
OTOH as soon as you decide to do w/o something is exactly when you need it
I seldom drop out of the 52 ring. I'm not very studly it's just very flat here and I'm fairly large so pushing the bigger gear is more efficient for me. However as local communities modernize their roads the relatively low drawbridges I ride over to the beach are replaced with bridges tall enough to let ships/sailboats pass w/o lifting. On THOSE things I do like to be able to drop to a small ring.