The Opposite of Impact Is Fluff
So, you’re playing D&D and you’re fighting some orcs. All the orcs are armed with feather dusters, so they [are] actually incapable of harming anyone. And your DM doesn’t give [experience points] for combat, so they’ll yield [zero XP] upon death.
This combat is a waste of time. You’re just rolling dice until the orcs die.
The encounter is shit because the encounter has no impact.
Impact: the ability to permanently change the game. The opposite of impact is fluff.