I don't think it's a good situation.. I have had a bad experience with it. We let a coach use our boy for lessons, days he wasn't suposed to be used and I would go to ride him, he would be being ridden when I showed up, to many lessons in a day (5 kids a day!!!!), it was ridiculous... My horse was NOT happy what so ever! So that ended very quickly and not in a pleasant way!
If I had too, I would only let select riders to.