Yup, for fun. That's the point of playing any game. It's to have fun. This seems loss in spirit of competitiveness.

$$$ - I set $1 for friendlies so my stadium is full. The small amount can help when you are short a few Ks sometimes.
Boosters - Useful of course.

I also suspect that when u have a player who is going thru a bad run, playing him in friendlies will make him get over that run quickly.