When playing on Ultimate Team they should be like a Stat upgrade or downgrade for every player at least in the biggest leagues or clubs in the game (Online Mode only not Single player mode)
For example lets say you have Jamie Vardy who is 82 rated
Hes been playing well and scoring goals and putting on good performances so the last 2-3 games hes played well hes stats will go up to 84 making his selling value up (But of course cap it to the point like no higher than 85)
However lets say hes played badly and not scored goals and hes even got sent off of for you hes rating goes down to 80 (Cap it 80)
I reckon this is a good idea for the game as it might the Transfer market more interesting and create some profit for the owners but at a cost of form and rating which can change after at least 3 to 4 games
The ratings should affect after 3-4 matches with each player so when Vardys whos been inform for you team has a rating 85 will go back to 82 (Default Rating) when hes played 3 games with the small boost for playing well.
I think this is a brilliant Idea to change Ultimate team and make it even more interesting.
Sorry If its long.