Before upgrading the Horadric Cube, Roy mainly used it to transmute souls.
In the system, different souls had different uses. As someone with a cheat, Roy naturally could not waste time deliberately nurturing the souls he needed. For example, 'fallen souls'. Under normal circumstances, it required a person full of negative emotions, greed, and difficulty satisfying themselves to give birth to such souls. In order to obtain such souls, Roy could either search for such people one by one or fulfill his demon duties and personally tempt others to fall.
He did this in the beginning. But ever since he had the Horadric Cube, he could transmute ordinary souls into the souls he wanted at will.
However, that was all the use of the Horadric Cube. The function of this item was relatively simple.