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...

>>3
PROTIP: The K&R book is kinda old. It doesn't know about C99 for instance, which makes it 8 years out of date. Pick up a more modern work on the subject and learn from there; C has got quite a bit less painful over the years.