>>43793007>>43791796Because you can use any move while using it, unlike something like Assault Vest or Choice Whatever. You can carry Sticky Web and Thunder, Stealth Rock and Stone Edge, or
>>43791816 with Recover, Lava Plume etc and have the flexibility to adapt on the fly. And on the example pokemon given, with good bulk as well as good attacking stats, if you just make them go first and circumvent speed entirely, you've got a 20% chance to effectively have a much much higher BST for that turn than you actually have. And since these pokemon are meant to have decent bulk or recovery or whatever, you're usually not getting OHKO'd, meaning you've got a 40-60% chance of activating it in any given match, add another turn on top of that if you dynamax that pokemon, which would actually give you decent odds of activating it at least once.
I'm telling you I've won multiple games off of quick claw Vikavolt shutting down a gyarados sweep or a hydreigon sweep. Normally unwinnable situations in that matchup, but if worse comes to worse and I find myself in such a situation, there's a 40% chance I might just win anyways.