stars is a vision of the quality of your players.
The higher quality gives you more chances to perform better and win games and titles.
Every season you promote, your (existing) players are 1* less for this new level.
More info about stars here
https://forum.topeleven.com/tutorial...-level-up.html

When you go up a level (promote) what benefits does it bring you beyond just being in a higher league?
it's the style of the game. Every new season you 're facing a new challenge, to build your team and win whatever is possible.

Yes, it's like starting from the beginning but it's like most of the games logic.
Find a new weapon and armor or increasing your xp, but you 're facing more difficult opponents