YUV and RGB and why?

For using color spaces to grade in, when do you use RGB and when do you use YUV?

My impression is:

YUV is for anything that ends up being for television broadcast.

RGB is for web media and films.

Is it as simple as that? What if that film becomes aired on TV? If it was colored in an RGB space, what happens when it's aired on TV with the YUV space?

I have been doing reading on different postings online, but I haven't read anything yet that drew definitive guidelines for me.