Just remember.....anything you say after hj has the last word, starts a new thread completely!
Most receptacles can pass through more current than they can source at an individual outlet and Ian is wrong...you can use 15A devices on a 20A circuit. Although, if you have some one thing that can monopolize the circuit's max current, it's sort of nice to size the outlet for that user.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013
For what its worth, twice a year, (Thanksgiving and Christmas), pretty much every burner on the cooktop, and both ovens of the double oven, are going full speed.
IN THEORY....a 15 amp equipment could have an internal fault, and since the breaker wouldn't pop until 20, damage or overheating could occur since internally, the equipment is designed to be protected by 15 amps max. This is a stretch of an argument, and the NEC apparently feels comfortable enough to allow it. I do understand that the Canadian Electrical code does NOT allow it.
I make the extra step and "pig Tail "all my receptacles rather than feed through.