Oh... I see. Thanks!
So it's pretty much useless + makes harder to calculate every time if the team gets to max fit before the next match.
You get 8 / 0.9 = 8.88 rests per player per day, so 0.88 extra.
For your starting eleven, that is 11 x 0.88 x 6% = 58.67%.
This means 58.67 / 15 = 3.91 greens for you starting eleven. Per day!