There are lots of good reasons to play music with other people, no matter what your musical goals are.
A significant percentage of people spend most of their time playing alone. Not just in practice time, but playing in general. There’s nothing inherently wrong with that, but there are musical skills that are only developed by playing in a group. Relating back to last week’s “big ears” post, the ability to listen and react is one of the most important.
There’s a big difference between practicing a part by yourself and playing it as part of a group. Playing along with a backing track can be a good first step in learning to fit in and blend, but a track never changes. After some repetition, you know exactly what to expect. But in a live setting with other players, even solidly consistent performances have variations. Playing with other humans forces you to tune in at a more detailed and dynamic level, even if the parts never change.
One of the highest goals for the aspiring musician is to be able to play with intent in the moment.
The part might be thoroughly practiced and planned in advance, but in performance it still has to be executed musically and dynamically. There’s no better way to develop that intention by reacting consciously to other players.
Maybe most important of all, though, playing music is one of the best things people can do together as a group. When a performance is at its best, it’s a collective experience shared by everyone, a way to wordlessly communicate and share an emotional connection.