Win bonus is one of the unanswered questions of the game.
The answer for this kind of questions is "better have than not"
I put bonus in my CH.L. & Cup games (except the easy ones) and in my critical League games.
set to lv1 bonus except finals where I set the max.
I also had some questions about the win bonus,
check this post
http://forum.topeleven.com/top-eleve...questions.html