On a normal day I don't use any. Some days I do a full squad rest, but just once a week or something. Other days I may give 1 to some specific players but not often.

If you try to train after you've played all matches with 22 players (also using more the subs and the ones who never play) you will be ready for the next day without needing any extra rests, with 8% on all bonuses (after it has decreased from 10%). Then a couple of trainings per position would put your team on 10% bonuses in the 4 areas. If you have an early match, you may not be able to reach this 10%, I always have my team between 8 and 10%, depending if I can train in the morning before my first match or I can't. But not a big deal. If I really need the 10% I would use some rests in the way I explained, but that's rare.