Forgot to say one thing that if a player only play in competitive match but seldom participate in training or friendly match, his form will deteriorate.
If you have entire team doing that they will eventually exhaust mid season and once this happen it is very difficult to recover.

Training and match have opposite effects:
Training increases player performance but reduce training efficiency.
Playing in competitive match decreases player performance but increase training efficiency.

Playing 2 competitive matchs a day is unsustainable by one team due to the lack of condition... unless you spend green packs every day so that your players can train in the facilities.
Some managers make two teams of 11 on shift to prevent this but it is expansive to maintain.

It isn't a concern if you have no CL or cup games to play though.