there is no reason to do this.You can cancel them if they set it in the future and you see it before it starts. I do this sometimes for opponents that are in the same Cup or CL as I am. They want to practice against my team because they know they will have to get by me at some point. I do my best not to allow that.
Friendly games have a different calculation and process. I have won friends who challenged me, 5-10 levels above sometimes
If you 're not gonna watch your game, that's good. If you 'll play, there is no reason because you can change your formation.When a final is approaching I will actually put up a totally different formation and tactics just in case they try that.