[Analemma_]

There’s a specific “Unix mode” you have to turn on to be in the compliant state, it’s not the default. Presumably among other changes this puts APFS into case-sensitive mode.

[Steltek]

How much stuff breaks when you do that?

[p_ing]

There's commercial software that will not run on a case-sensitive file system, such as Photoshop.

If you're using 3rd party software, you don't want to format your default volume with case-sensitivity enabled.