I'd consider very few pieces of equipment to be utterly useless, and those would be the ones with bonuses that are literally unable to be used, like a two-handed weapon with a Shield bonus. Many of them are simply unoptimized for a straight one-class single-focus build. But this can come with its own perks - I noticed the other day that my fighter had two rings that, among the bonuses I was using, both had Telekinesis on them. She's become my retrieval expert at no extra cost simply because of 'bad' equipment. I rather like it.
