I don't really need to do this as the majority of the advice above is good, but I feel it will not hurt to have it reinforced by someone that was/is an engine professional.....
NOTHING GOOD HAPPENS WHEN AN ENGINE IS IDLED.
Diesels don't mind sitting at all.
Carburetor engines only have trouble because of fuel left in the carburetor. If you deal with that by draining or running it dry, then that is not a problem.
The people that advise that you periodically run an engine or genset, are the same people that sell parts......
Matt