Dedicated circuits

@jea48  It's against building code to install 20A outlets on a 15A breaker.  You may be correct that the 15A breaker would trip, but do you want to risk your home insurance not paying out after your house burns down?  Just follow the code and be protected.  It's there for a resaon.  

@bigtwin  , actually it was me, not @jea48  who was wondering about a 15A circuit breaker on a 20A circuit.  Anyway, I am not trying to be argumentative, I was just thinking that if the circuit breaker is designed be the weakest link in the circuit I thought that making it a little bit weaker could only be further protection for the circuit. 

I did a search and found this

Should a 20 amp circuit have a 20 amp outlet?

The amperage of the outlet must never exceed the amperage of the circuit. According to National Electrical Code, only a 15-amp or 20-amp electrical receptacle can be installed to a 20-amp circuit.

That's incorrect. A 15A outlet shouldn't used on a 20A circuit.

@immatthewj   A 15A receptacle on a 20A breaker is not an issue as any 15A appliance will never exceed the wiring in the circut.  The reverse of a 20A outlet on a 15A circut is where the potential of fire comes into play.  We assume the breaker will trip and protect us from harm, but what it it doesn't?  That's why we don't push our luck.  Cheers.

You can plug numerous items into a 15A receptacle that exceed 15 amps, portable heaters come to mind. My Skilsaw. The outlet is undersized for the circuit, and the potential load(s).