Need a report for plugin usage - plugins that are actively being used and who is using a the plugin. Currently there isn't a way in JIRA to see this information and no plugin that would perform this action. Sometimes plugins are requested and installed but there isn't a way to see a list of the plugins that are actively being used and by whom. Having this feature would make it easier when doing an upgrade analysis or an analysis of the system and plugins installed.
that's a tricky thing and you will have to look at different places depending on the apps you're using. For example an easy thing to find out is the usage of custom fields provided by third-party apps. Or for example if you want to find out wether you are using additional workflow extensions (conditions, validators, post functions) from different apps in your workflows or not, that could be achieved using the workflow report of an app we at Decadis are offering on the Atlassian Marketplace called Admin Toolbox for Jira down to the very specific transition or you go through all workflows / xml exports manually. And for different other offered features by apps you may also have to skim through the log files of your system. It's not as easy as it is in Confluence with the macro usage report. Maybe we can be of bigger help here if you have examples for us which app you want report on.