With respect, the problem for people who prefer to choose a cabin rather than have one allocated, is that they may end up in a "better" or, as Princess word it "comparable", location that isn't desirable to the passenger, ie starboard side when scenic cruising or the sun/shade is predominantly on port side, maybe an uncovered balcony when you want civered, or more central but under the pool deck or a walking/jogging track, over the theatre or a noisy bar, or by a lift lobby where people gather and natter at all hours, under a seawalk or at the rear of the ship with early morning anchor noises that they may not appreciate.
I appreciate that not everyone is as picky but I for one would only take "pot luck" if the fare was super cheap making the holiday a real bargain not to be missed. Just my view.