In general, you may want to kill them for good: unregister all events, reparent them to a hidden frame and so on.
But sometimes Blizz make bars (esp
MainMenuBarArtFrame) do more things than they're supposed to do, for instance, at some point in the past
MainMenuBarArtFrame was used to update either currency or rep tab on your character frame, so if you unregistered all events, you wouldn't see one of those tabs there
I kill them all, but I keep events on
MainMenuBarArtFrame, haven't caused any issues in years. Bartender hides most of them w/o touching events.