I shave as much leg as will be exposed. This means 3/4 leg every other day in summer (full leg if wearing bathing suit), up to the knee in spring when I'm wearing mostly skirts, and barely at all in the winter, unless wearing anything shorter than a full length skirt. I do it because I like the feel of it and prefer the look of my legs without hair. I don't do it more often because I'm lazy and it's also warmer to have leg hair in winter (though it does sometimes play awkwardly with dress pants and I may start shaving in winter, too, as I spend more time in professional clothing.)

I shave my armpits because, again, I prefer the look of it and I also think they get less sweaty when I shave. But, again with the laziness when I'm not wearing sleeveless clothing with regularity.