the gaining of friendlies and training is about the same (condition loss/progress).

The others are more managerial.
For example in low levels the stadium is small and the tickets price is cheap so it's not worthy to make friendly games.
When you pass lv10 and have some good facilities (a stadium of 150 K') , then you can get some good money from friendlies.
Of course you must have some extra reds cause the injuries are real.

If you 're making too much friendlies instead of training, your drills won't increase much (the 1-2-3 whistles & then the globe).