Futuball is football, but things are different than back in the early 2000s.

As players are now robots with DNAs injected into them, they only consume their career energy (typically around 250 league matches from when being built) when the play in matches.

So do not play your best players unless they are ABSOLUTELY vital to play to get a crucial win. You are much better of in the long run, by playing some of your lower squad players and use their career energy. This way you can save your best players for when it really matters and make their careers last for many many more seasons. Having a wide squad has never been more important.