I would say it depends on your dogs agenda and how much time you have for grooming (if needed) after a good roll; you would know best.
These are my deciding factors that determine if Bobby gets to have a roll:
If he is running around and stops to roll without putting too much thought into where he is rolling, I always let him. If he spends even a brief second sniffing before he rolls I always stop him because he just wants to roll in something gross, stinky, or dead. If it is mud, unless I plan on giving him a bath afterwards, I don’t let him (I am a party pooper). I always stop him if he wants to roll in an area that is questionable because he or the humans in our family could be exposed to something irritating or harmful.
