Simple issue: you create a vector shape, and then another one in the same layer, and you want to subtract the latter from the first. There's a "mouse" way to do it (on the "Path operations" button on the top), and there used to be a "keyboard" way to do it, with the +/- keys on the numpad. I used it all the time, it was very handy.
Since Photoshop CC 2015, it doesn't exist anymore, and it's very annoying. Please, Adobe, put it back! Thanks!