Having discovered the mirror modifier I have been assuming I should always use it when modeling a symmetrical object.

For instance, take a simple stool. Is it more efficient to model one half with a mirror, or model the round top, and one leg, and then copy the leg around to each quarter?

Can I make a mirror of a mirror and model just a quarter of the chair? Should I?

Basically I am asking for alternatives work flows to mirroring, and the relative merits of them.