Unless I misunderstand @RosinBag, The context is not practice, it's checking tune, i.e. is the GEAR doing what it's supposed to. So if you know you failed to execute a good shot, you should definitely NOT put any stock in that arrow, because it doesn't reflect what happens when you do your part. Obviously you can't make a perfect shot every time, and for the purpose of something like determining max ethical shot distance of course you can't discount a flier, but if checking out your equipment, you shouldn't be making decisions about whether you're in tune based on an arrow you know was a bad shot.
No, he said he did that during every practice session. Not just setting up his bow. He just got through discounting one members practice because he said a 3 shot group was useless. But went on to say that he didn't count bad shots in his group. Lol.
I learned pretty early on that trying to shoot tight groups at the same dot was counter productive.
One shot per distance at a different dot was more practical for me, as every shot counts. Just like in my hunting situations. And I didn't waste my time or money replacing cut fletchings, busted nocks, or damaged arrows.
I've never gotten more than 2 shots at live game, so that's how I practice.