Could someone please help me understand the difference between 用不了 and 用不着?
用不了 is another way of saying 不能用 “cannot use,” e.g., 我用不了那个PC软件，因为我的电脑是苹果电脑。(I cannot use that PC software, as my computer is an Apple computer).
用不着 has more of a sense of 不需要 “don’t need to,” e.g., 这件事，他已经知道了，用不着再通知他。(He already knows about this matter, there is no need to contact him again.)
用不着 also has a sense of “have no use for/is no longer useful,” e.g.，“那本字典用不着了，还是网上字典快多了！” (That [print] dictionary is no longer useful, online dictionaries are much faster!”) Note that this is different from 用不了, as one can still use a print dictionary, but it’s usefulness is put into question with this use of 用不着.
Hope this helps!