It hidies attributes of players you know little about. Say your in the EPL, you will most liekly know all 1st team attrbutes so they will be displayed, but its unlikely you will know hwo good their u19s are so they will be hidden except for a few key stats and in order to uncover them you will need to scout them.
off is far easier.
Although if you want a challenge leave it on. If your a proper hardcore LLM youre meant to leave it on