You're normally "guaranteed" not getting a lower category room, but the hotel's room categories could be listed, for example, as standard no view, standard view, deluxe no view, deluxe view, grand super deluxe no view, grand super deluxe view. If you reserve a standard view room here and it's not available, the hotel could upgrade you into super deluxe no view (three categories higher), when you would have preferred deluxe view (two categories higher) or worse, you reserve deluxe view and are given grand super deluxe no view (one category higher) when you would have preferred standard view (two categories lower).