Unless you make the PS under different names and phone numbers, one or both will probably get cancelled. Disney doesn't like you to hold more than one PS for the same time.
It's only polite to cancel the one you don't want to use, but there is no penalty for not doing so (unless it is for one of the restaurants that charge deposits. Most don't). And if you don't cancel until just before your PS time, it probably won't make much difference if you cancel or not. There wouldn't be time for anyone else to make a PS for that restaurant & time anyway. If you cancel a PS or don't show up, it means the restaurant can take more walk ins or have a shorter wait time for walk ins.
But by holding multiple PS for the same time, you deny others the opportunity to make PS in advance. Iin the whole scheme of things, that's not a terrible thing to do (just selfish), but it isn't very nice, either. JMHO. YMMV.
Best wishes -
Best wishes-
