One example of this is computer games. There are games like StarCraft 2, Diablo 3, where server is required even for solo-playing and it's not possible to play

One example of this is computer games. There are games like StarCraft 2, Diablo 3, where server is required even for solo-playing and it's not possible to play offline. I think that one of the reasons is to make it harder to crack a game (as you would need to re-implement server) and to make a cracked game objectively worse (as your implementation will not be as polished).