Why are custom VAEs even required?

This is an automated archive made by the Lemmit Bot.

The original was posted on /r/stablediffusion by /u/barbarous_panda on 2024-06-28 07:36:03+00:00.

So a VAE is required to either encode pixel image to latent image or decode latent image to pixel image. Which makes it an essential component for generating image, because you require atleast a VAE to decode the latent image so that you can preview the pixel image.

Now, I have read online that using VAE improves generated image quality, where people compare model output without VAE and with VAE. But how can you omit a VAE in the first place??

Are they comparing VAE that is baked into model checkpoint with custom VAE? If so why can't the model creator bake the custom (supposedly superior) VAE into the model?

Also, are there any models that do not have a VAE baked into it, but require a custom VAE?