I tent to make only one large room. Rich and clean where to do everything.
This situation is not really realistic since a stone cutter bench is suppose to be really ugly and create dirt. Same for smelting etc...
Would make sense to make them really ugly and create dirt over time.
Certain benches already contain an "inherent uncleaniless" attribute which means even if you clean room is won't be considered a completely clean room due to their presence.
It is not really significant.
The actual implementation is less realistic then it could be. Braking stones should produce tons of dirtiness and the noise of smelting etc... should be translated in ugliness.
As it is right now player is not pushed towards for interesting designs of colonies since a signle room for everything is enough.