Official comment
Well, for starters, different fixtures will have different functions or uses. A strobe doesn't have any colour or fading. The "simple" fixture types have their own, more simplistic, macro functions.
rekordbox lighting isn't designed to "light a bar under the table" - all connected fixtures are "part of the show" and respond as they are programmed within the macros. There's no static function (but there have been many requests for it, so hopefully in the future!).
You are always best to assign the fixture to match its device type, as there may be more for bars over pars in future updates (eg. pixel / segment mapping).
If you open any lighting macro you can see what is assigned to each of the fixture types, and even change them as you desire.