If I may pop in, perhaps this automated function wasn't included because of all of the 'hiding' mechanisms within Bandicam (that is, minimizing it out of the way and hiding the control bar in Rectangle On A Screen Mode) - they probably thought most people would just do those things, then use the hotkey to begin a Full Screen Recording after nothing is showing - but I like your idea; it sounds similar to how Corel's ScreenCap works
The problem is, for people that want to Record the Bandicam interface (to show updates/changes/settings/Tutorials/etc), or who want to record a portion of the screen and have the interface running for indicators/changes/control/etc, these people will have to 'un-minimize' everything, every time they want to record the screen. It is sort of a 'six-of-one-is-half-a-dozen-of-another' case.... For now, perhaps Minimizing everything before recording will suffice?