You gain one alternatively.
So if the previous upgrade you got a coach slot then the next upgrade you will be granted a player slot, and vice versa.
Check on the imagine in the facilities menu.
https://puu.sh/sIHST/7da7073498.png
It helps when you want to replace your main player with a better player from the market ! And for streaming too, this is a secured income ! And for training !
Dunno if you saw my edit on my previous answer*
here is the edit :
Check on the imagine in the facilities menu.
https://puu.sh/sIHST/7da7073498.png