Wouldn't the use of a belt defeat the purpose of training to become stronger? If, by wearing a belt, one becomes stronger then subsequently removes the belt to lift the same weight, one would not have gotten the benefit of training to strengthen the muscles which the belt is intended to support. Without this benefit, one would then be at greater risk of injury without the belt. I see the same argument for straps.
I'm thinking of a sprinter using crutches to train. He would most certainly not become stronger or as strong where the crutches support him.