OK, so, within two postings we have gone from they dont think much about what they kill, just wanting to have dinner, to rather shrewd behavior of eliminating competition. Im willing to believe that happens, but, would tend to believe it is a very, very rare thing. Most predators probably expect a meal at the end of the effort it takes to overcome a small prey animal, and a least a primitive notion that chances of success against another, equal predator are less.
Stans owl would more than likely have begun consuming her kill (the big ones are females) had Stan not shown up.
They may eliminate competition. But, except in a case like this one, Id wager there is always a meal at the end of it. The calories it takes to pull that off are too precious to not replace.

Best,
Ted