In my opinion and my following words supposed not to force anyone to accept it but anyway see what I'll say:

*- If you are strong team and your team is always full of 5* player and more than 5* players then you can use any fixed formation/tactics for all matches and during the whole season.

*- The stability (in my opinion) is a key element in making the victory or the continues wins; If you decided to use a specific formation with fixed tactics and also specific player in main squad for along time, it will be too much useful and will generate continues win.

This the result of 13 season experience in this game.