For example, at Netflix as a manager I don't "veto" any proposed vacations, because my engineers do not propose vacations -- they tell me what time they're taking off. It's their job to make sure that's not going to be a surprise to anyone covering for them, and it's not my job to check that they've done that work.

As for being careful not to be the guy who takes too much vacation ... putting aside the fact I have people reporting to me who aren't guys, there are people on my team who take two days of vacation a year; there are people on my team who take ~6 weeks of vacation per year. Nobody here seems to care much.