bits manipulation (C)

I'm an autodidact and I have programmed in C for one year now, but never studied this topic. Apart from operating systems or embedded systems, when do we need to manipulate bits in 21st century ? If you could give some examples...

Too bad bit manipulation is slow as hell.

checkSign :: Int -> Int
checkSign -1 = -1
checkSign 1 = 1
checkSign 0 = 1
checkSign x = if x < 0 then x + 1 else x - 1