IMHO there is no big difference between level 4 and level 5 as i could see.
What if the difference is an extra week of training per season? You probably wouldn't notice it very much, but the difference would still be there.
For the average user, it wouldn't matter much. But for someone training U21 players, an extra 4 weeks of training between 18-21 would be a nice bonus... Especially if you are doing 1 position training.
Run of the Mill Canadian Manager