File Size and Community Tools

Trying to cut down on file size is actually pretty easy with some community tools.
One’s VRWorld Toolkit will give you a full report of all the files that are being uploaded to VRChat after every build, so after testing your world or avatar once, it will give you a full list of everything that might be taking up space, and will also gives a lot of other recommendations that are massively helpful.
EasyQuestSwitch is another helpful tool, though it is for worlds only.
It’ll let you set up a bunch of options for swapping materials, settings, or active GameObjects between the two different versions, though its UI might be a bit confusing at first.
Lox's AssetBundleStat is another way of knowing what files are taking up space, both in file size and vram size.
This one is browser-based, and you'll have to select a built file of your world or avatar, but it will give you direct paths to where Unity stores those built files.