From David OReilly.com:
It's funny how people follow rules without understanding them. Most electronics companies have stopped making CRTs a few years ago.This is a subject which crosses my mind the more I see new animation work coming out. I’d like to share it in the hope its of use to image makers and viewers alike.
Everyone in the business of filmmaking is constantly aware of the rule relating to the Safe area (also called TV cutoff). All design for television is made with an invisible border which clips about 20% of the image. It’s a long established rule that all movement must take place within one border, and all text within another.
This rule is, in my view, completely outdated and unnecessary, and may be officially forgotten about immediately. It simply lacks any practical application considering how most video is viewed today, digitally, online and on modern screens.