Are auto-hiding floating headers bad?

Many websites have headers that are always on-screen when you scroll up, but auto-hide when you scroll down.

I hate them personally because the screen space they would've used up if they stayed permanently on-screen is terrible to use; if you accidentally scroll a pixel up it'll hide a few cm of screen space, and you have to do a little scroll up/down dance to get that screen space back.

Are there any studies on them?