So if any important player in the squad gets injured, their performance deteriorates. PSG does not have this problem. They have many talented players. So even if a player gets injured, they can maintain their performance stability.
In my opinion, the biggest advantage of clubs like PSG and Manchester City is that they have a lot of money to spend. So, if they have a player or players with a prolonged injury, they can easily go to the transfer market when it's open and buy a good player. These are clubs that, if they start the season badly, the coaches note all the problems and, in the first transfer window
they buy very skilled players for those positions where the coaches perceive problems. Unlike other clubs without great economic power, who, even seeing these errors, won't have the money to sign expensive players for those positions, PSG benefits even more because they are in a league where other teams don't invest heavily in their squad.