For me it has nothing to do with being a professional. It has to do with not needing 100 photos of the same bird standing, sitting , etc. Of a bird is about to fly, I will use pre-capture and/or take way too many shots when he continues to sit there.That's really a philosophical question for each individual photographer rather than a tenet that should be universally accepted, though. I would never pass up a shot because it wasn't perfect. You never know what you're going to catch. Maybe if you're a professional who has a very specific shot in mind, that would work, but how many people here are full-time professional photographers? What percentage of wildlife photographers actually make money at it?
BUT - it is valid to think about when, where and how much one is shooting as it relates to how many images are actually worth keeping.