>>1992224tops: super casual coasting, upright allows good traffic scouting but personally I always use the ramps
ramps: see above or also just a good alternative to hoods to give your grip a break.
hoods: best all around position, going fast, climbs, whatever. use it when figuring out your stem height and reach.
hooks: fast descents, lowers your body and best braking. also good alternative grip for normal riding.
drops: good for laying down power in a climb, in or out of the saddle. also good for strong headwinds.
the height and tilt of the bar is much less forgiving than other bars, there's like one position that works and dialing it in takes a lot of time and discovery.