It's at LONG distance where the extra shot extends the range by increasing pattern density. Not in HD where quick followup shots can be MUCH more important than hitting Bubba with three times as much ordnace as needed, and maybe his friends not at all because you're still recovering from recoil.
My practice comes from living in the country, where the burglar gun and the coyote-across-the-fence gun tend to be the same. Thus, the first shot is #4 for pellet count, followed by three 2.75" 00 or 000, and one 3.5" 00. As for recoil recovery, I've rapid-fired everything I use except the 3.5" 00 magnum 18-pellet load. It stays last, but it stays in because I really liked what I saw when I tried it on a plate rack. (I jerked it a bit low, missed the plates and knocked the rack back a couple feet, causing all 6 plates to surrender - I'm pretty sure that'll stop anything that finds its way to my door.)