The ability to pause is extremely important in games (at least single player ones).

I hate when games are into multiplayer modes even when played in single-player campaign (e.g.: Generation Zero) and thus cannot be paused.

Another thing that I hate in this regard are unpausable cutscenes. I remember when I was playing The Witcher 3, that at last there was some cutscene advancing some plot point, and right into the middle of it The Wife™ would barge in telling me something important that would require my attention... but I cannot pause that scene so I had to miss it while I listened to her. Why, oh why, devs hate pausing cutscenes so much??