Why do Chess GMs need coaches? Today chess.com did an interview with Carlsen's coach.

Someone like Carlen or Anand, why do they still need coaches? Their Elo is higher than their coaches, they can use engines to analyze the games, and they can beat their coaches in practically every game, obviously they know more openings than anyone in their room.

I understand that someone hires a coach to get better, or in other sports you do that to stay in shape, but this is chess and there are computers if you need help, i guess all the coaches use them, so why hiring them? What is their major role? Do all GM's have coaches? (including the ones who died, Fischer, Capablanca etc).
I don't know which person you are referring to, or if the exact word "coach" was used, but GMs like Carlsen don't really have coaches in the sense you are probably thinking of; they have seconds, who have the following functions:


Opening research. This might mean performing general research, or looking for particular weapons that are likely to be useful against the upcoming opponent, in this case Anand. Doing quality opening research takes a lot of time, and the player is better off paying strong GMs to do some of it for him them spending all the time on it himself. Also, they can spend time during the match doing further research based on the games already played, which the player doesn't have time to do.
Adjournment analysis. This is not really relevant anymore, but in the old days many games would be adjourned overnight, and the players' seconds would analyze the adjourned position all night and present him with their analysis the next day before the game resumed.
Training games. If a player has an opening idea, he can try it out against other players and see what sort of situations result from it before using it in a live game. This is often more relevant than playing games against a computer.
Moral support. Don't underestimate how much nicer it is to have a team of compatriots that can cheer you on when you do well or pick you up when you do badly. They probably also do other things together like exercise.