So I did test these with progressive on so that those who use it know it works with it.
The progressive fatigue settings on xp gain in drills differs from its impact on games. From a training standpoint only, it impacts the amount of XP earned for players in those drills.
I personally have never messed with auto subs and the fatigue slider because I have always felt they impact more than we know. I have no evidence of this, just my observation in games.
Using this with progressive fatigue off will increase the amount of XP earned by your players in a season. Nothing is tainted by this other than you may see a bit more inflation of ratings. Something that no matter how low these XP sliders went, still lingered.