The game ceases processing those matches and leagues. It won't calculate league tables of the deleted leagues, and it will speed your processing up. If you subsequently get relegated into a league you deleted, you lose your job.
That's not so. I'm a very low league manager and 10s would be way too high for my level. But at such a low level they do tend to be better than my white players so I have to avoid the temptation to sign them. What does tend to be the case is that their PA is close to their CA from what I've seen, so they won't develop. There could be exceptions that I haven't come across.
It's fiddly, but you can take control of the Youth Team for a day, rest the said youth and then Instant Result the match (assuming you have a suitable skin).
Emma Hayes would not be impressed with the sexist ignorance on display here. The filter is in the pre-game editor; it ought to be in the game. I also use FMRTE for that facility.
I, like many, complained when the game was first released months ago, but I haven't had such an issue for a long time now. I hate to be that guy, but it sounds like despite your protests, you use a tactical exploit.
I use it for my level 13 save. I find it MORE feasible given I try to create a 'realistic' narrative in my head. Our (two coaching) staff are amateur, we have no analysts, I'm unqualified - how on earth would I know if my midfield destroyer has 2 for tackling or 4? The pizza chart shows me that all my lads are hopeless, but some are determined and work hard or can run a bit and so on, and that feels good enough for me.
It's not 'Potential' if it can increase, so that is suspicious. Do you have the IGE to check if FMRTE is in error? Some skins have the facility to show CA/PA also.