Originally Posted by Fat Borat
Because "impact", while still somewhat opinionated depending on context, is quantifiable
But "impact" on what? 'Impact' has to be impact on something. And impact implies change. You can't, for instance, talk about Snorlax's impact on the OU metagame, because Snorlax has always been OU. You could talk about the impact of someone coming up with a particular set, but that's gonna be of historical interest only anyway.
You could mean the impact of putting him on your team (replace another Poke with Snorlax, how does it change your team), or the impact he has upon the opponent in battle. Both of those would be relevant. But whatever you mean, to say 'impact' alone is meaningless.
Or perhaps 'effect' or 'influence' would be better words.