For an extension of type xar, it is interesting to know what pages it brings in the wiki when installed.
One of the ways to have that today is to look at the install log (if the page was installed) to see what pages were created on the wiki, but that is cumbersome to read and I think it will not contain everything, for example in the case of an upgrade all the pages not updated during the upgrade will not have entries in the log.
Currently it's possible to know that a page comes from an extension by looking at the history of that page, but there is no UI for the opposite operation of seeing all the pages of an extension.
Whether this list should be displayed only for installed extensions or for any extension doesn't matter that much, I guess, if for security reasons the not installed extensions cannot be listed I guess it's fine, it's mainly needed for installed extensions.
This would be similar to the "installed files" that (some) package manager UIs of Ubuntu have.
The xar entry type (in the sense of https://extensions.xwiki.org/xwiki/bin/view/Extension/Extension%20Module/Extensions/XAR/#HStandardtypes ) should also be displayed next to the page in the listing as it's interesting for understanding the behaviour of the extension.