>>2772756>Is there any particular reason why this is done?Strictly speaking, no, you can use whatever you like.
In reality there aren't very many unique vaes. For the purposes of this thread, there are pretty much two. The "stock" stable diffusion one and the anime vae that ultimately came from the nai leak.
Also it's worth noting that some models have the vae baked in. How do you know? It should say as much on the model page.
