I have discovered the True Tactic of preventing tired players in many games

[Cat Harrison]

Now now, let's not be rude.

It is true that if you are only in 2 competitions, your players will be less tired (and get less injuries).
However, you will have less $$ from competition prizes, and truly that's where the best income is..
also less boosters if you have less games to attend.

[Siddharth Shanker Singh]

less boosters if you have less games to attend.

In fact you can earn more boosters by playing friendlies...