In thinking about my choir, it's amazing all the different ages and economic classes (our racial diversity isn't huge, but it's there to a small extent) and political opinions you can get in a group of about a hundred singers. Yet we work together and make something sublime, or at least that's the aim. We subsume our individual identities in order to produce something that has no purpose but to feed the soul.
I spend three hours a week in rehearsal, plus extra practice on my own occasionally. I could easily spend those three hours writing, adding another 500-1000 words to whatever projects I have currently going. But, based on the year I did not have a choir, I found there's a sort of synergy between the two activities. I seem to need both. I need that connection with others that singing gives me; perhaps because writing is, for the most part, a solitary activity. You don't get connection until the story or novel is complete and people read it. I've heard people say a piece of music isn't complete until it's performed, but I don't think that's true for the singers (or instrumentalists) involved. In a way, every rehearsal is a performance. A performance for whom? I don't know. Each other? Ourselves? Rehearsal is very different from a concert performance, but I feel it's a vital part of the process.
When choir becomes too mentally consuming, for instance when a concert is near and my brain radio is taken over with music, I find I usually can't write, even if I have snippets of time in which to do so. So I think some of the mental/emotional energy used in these activities is also the same. Both of them, if I may be poetic for a moment, feed the soul.