Hello James -- The file upload size limit was one example. There have been other instances when having the ability to add nginx directives would be beneficial.
However, for the upload size example, specific apps would include ghost, wordpress, peertube, and possibly nextcloud. Applications where users would regularly upload files. I believe by default it's set to unlimited. But I have use cases where modifying the limit would be beneficial.
Not a huge deal. But it's something I've been exploring and figured I'd ask. Thanks to everyone for reading.