I stand when I can, but after a few beers or it's middle of the night it's better to sit, less splashing around ;-)
(sorry ladies, but someone had to say it)
I'm skin and bones, don't ride a road-bike, and studied accountancy - therefore am too boring to be of any interest ...
... but just for the Hades of it, I like standing to climb - including when on the bike. It suits me. A couple of years ago, standing for 100 metres and the arms etc would want to rest. Now through doing lots of it (climbing), can keep standing for considerably longer (e.g. all of Checker the one time I went there, bottom climb of Sheoak), short sit if need be, then up again. Increased time on my rower over last year may have helped.
I get up.
I'll get up on the flat - accelerate!
I'll, get up on the hills - (well) desperation!
I'll get up going down - I wanna go faster!!!
What do you want to do?