I tend to not use any character that I can't control manually, at least in the games where manual control over your party is the norm. That would mean Gau and Umaro in FF6. They sometimes get to take part in some of the dungeons where I need three parties.

Other typical bench warmers for me are Nanaki, Cid Highwind, Cait Sith, Selphie, Amarant, Quina, Khimari, Wakka.