Welp, believe this or not, I've read where serious riders shouldn't 'do' ballet. Something about the muscles and movements counteract each other. It's been a good 5-6 years since I heard of this. I asked on another horse board if anyone had heard of this and surprisingly, quite a few had.
Michael Poulin and his crew took ballet. I heard him tell the story in a clinic. He said it greatly improved their proprioception, coordination, balance, etc. He did mention that they told the instructor beforehand that they needed to do everything flat-footed and without turning toes out, but he said it was incredibly helpful.
He can still do some moves, even wearing riding boots in an arena.
I do Crossfit and if that doesn't mess with riding then NOTHING will! As a side note: I'm schooling 4th/PSG dressage on a very difficult to ride horse and the owner thinks it's beneficial that I am doing Crossfit and am very strong otherwise. I don't get tired at all riding and I feel like I have better control over my body since Crossfit. Now, there are some days when my muscles are really sore and that makes riding a little more of a challenge...
When I took a short break from riding a picked up ballet as my activity. Granted, it was only once a week and only lasted for a couple of months (I couldn't stay away from horses for too long ), but it did help my riding some. I got more flexible and limber and it really helped me when my instructor had me do exercises to help my seat and leg.
If i smell like peppermint, I gave my horse treats.
If I smell like shampoo, I gave my horse a bath.
If I smell like manure, I tripped.
I've just started ballet class 2x week and love it! I even got a leotard, tights, and little skirt to cover my butt....
So far I love it. I'm middle-aged, I guess, so no chance of me becoming a professional ballerina; my body is fully developed so there's only so much turnout I'm going to get. I don't have flexibility in my ankles (heels down has always been an issue) so have a hard time with grand plie in second position.
The workout is great and it inspires me to try to be more graceful, which I think would somehow help me in the saddle (but I'm not sure how yet).
I don't know, I think that if you like it and it is fun and interests you then you should do it!