You cannot JAM, freestyle groove, just based on riffs, rhythm and common ideas if you aren't using your war. Or at least you won't be very good at it.
There are about 100 different things I love about playing music. Some of those things involve playing alone and some of those things involve playing with other people.
But one of the most awesome things I love about music, is when I am playing with at least one other person, the more the better, really, and everyone is a good or great player and what is happening live is working out so well that the resulting music ends up being even greater than the sun of it's parts. It is a magical musical place that I can't get to by just playing by myself. I love playing with awesome musicians and knowing I can hang in just about any musical situation thrown at me. Maybe I won't be the best in the group but as long as I feel like I am adding to the sun instead of taking away from it, then I feel like the tend and tend of thousands of hours I've spent playing music in my life is we'll worth the time spent.
And besides that, playing with others, in a musical situation. You are happy with and are contributing to, is simply just fun.
I don't always need to involve playing with others to be doing something I feel is worthwhile for myself musically, but it is also one part of music I would NEVER get rid of or overlook for any reason. I know how valuable it is and how fun it is when the situation is right.
One thing I've learned in all these years though, is that there will ALWAYS be good musicians around to play with so I spend very little time and have zero patience or interest playing in a situation I am not entirely happy being in.
It is just too easy to move on and find something better. Tons of great situations out there if you just look, or you can apply put your own deal together if you want.
Playing , jamming, whatever you want to call it, can be one of the most rewarding parts I love about all things dealing with being a musician. It can also be one of the worst, but so what? In those cases, I just move on.