We should list our different exceptions and explain when to use them. Maybe a wiki page? Also the naming should be more consistent.
I'd love to see more and updated dev documentation on the wiki. We could update/enhance the Devbook (https://wiki.koha-community.org/wiki/Developer_handbook)
If you give me some more pointers, I or others might be able to help in writing this up.
What kind of pointers do you need? We need to make Koha::Exceptions namespace more consistent: the naming, the tree, the display of the exception (parameter, errors, stacktrace), etc.
It sounds more like a clean-up than a documentation job.