Jenkins has the option to allow the user to discard old builds. When the checkbox is ticked, two fields are displayed allowing the user to specify discarding builds older than N days and/or to keep only X builds. However, if neither field has any content entered, no builds are discarded. This behavior is non-obvious to the end user; they may believe that not specifying any fields means that ALL build results will be discarded (i.e. a CI job is running and it doesn't matter why it failed, just that it failed).

I would recommend that a warning be displayed letting the user know that no builds will be discarded if all fields are blank.