This plugin collects anonymized usage statistics for known ImageJ modules (commands, scripts, etc.).
Statistics are accumulated every time a module is executed. Once per hour, and when ImageJ shuts down, the statistics are flushed (i.e., uploaded) to the ImageJ usage server with an anonymous but unique user/machine identifier. It is not possible to tell who a user is from the identifier, but each user/machine combination is guaranteed to have a unique identifier string, to facilitate computation of statistics such as: "How many people used such-and-such command within the past 12 months?"
Collection of usage statistics is optional, and can be toggled in the Edit > Options > Privacy... options dialog.
Such information is very useful to the developers in prioritizing bug-fixes and new features, as well for continued funding of valuable functionality.
For further details, see Usage on the ImageJ web site.