A person who learns and plays alone is at a serious disadvantage (even if only briefly) when it comes to playing with others. If nothing else, one tends to develop bad habits; it is easy to be too forgiving of oneself.

I remember some years ago listening to a technically very good fiddler on stage at a folk festival. She was being backed by a guitar player who had to jump time over and over again to follow her. It was painful to hear.

Our band leader/fiddler also heard her and promptly invited her to join us in playing for dances. She started coming to practices and given her inherent ability quickly became very good.