If Volcarona stands to sweep the entire team at +1 then why would you risk switching it in when you can just sac whatever's facing Scizor to Bullet Punch, or nail it with whatever attack hurts it most if it opts for U-turn instead?
Exactly. What would you gain from switching Volc into an attack that could deal fair damage (even more if Rocks are up) when you can sacrifice the Scizor-weak Pokemon you have out to give Volcarona a free switchin, allowing you to Quiver Dance on the switch and sweep? It makes no sense whatsoever.