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...

>>2
Fine, thank you, I will look at some source codes. But before, I'm searching some good documentations/tutorials about bits and bits manipulations ; I have learned C with the K&R book, and maybe I'm dumb, but their code examples and explanations weren't very meaningful to me.