I like auto-play in my opinion.
Example, I’m taking a bathroom break, I hit the auto and the game does the quests itself.
When I get back, I’m done with that quest, and I didn’t even have to hit the attack button.
Just my opinion.
Also, to cancel it, just keep hitting it when it turns purple (purple = on).
The system will register that you don’t want to do auto and it will leave you alone.