I find it hard to configure custom jsp: you have to know the name of extension and the name of the jsp file to configure it correctly. This is specially hard if you have a lot of extensions each with custom jsps. Additional there is no way with web UI to find what custom jsps are there - it's possible to see only list of extensions  - and to see this you have to go every time to admin page AND you need admin rights to see it. It would be much simpler to have list with all installed custom jsps.

I can find also where is Usage field from extension install.xml to see in web UI.