Well even if you win the match, if there are players that didn't perform well, they may drop in morale.
I usually offer my players a win bonus when ever the upcoming match is very important. Otherwise I tend to drop it entirely and save up the cash. I am a player who mostly relies on proper formation and tactics so I don't always supply a Win bonus nor do I try to get my Team Bonuses to 10%.
ALTHOUGH as others have noticed as well - It's not hard to keep the bonuses at 10% once you get them there. You simply should not skip a day of training.
But as I previously mentioned in the Rests paragraph of my previous post - There are many ways to play the game.