When you play with multiple wow windows open and with mouse focus tracking it helps to set the windows taskbar to "autohide". But it often happens that you trigger some kind of info on the other wow clients that leads to the taskbar icon flashing, leading to the taskbar to reappear.

There is an incredibly simple "Nostartbar" addon that simply overwrites the function to do that and only consists of:
FlashClientIcon = function() end

It would be nice if an option to enable / disabled this on all clients could be added to Ema for convenience. This isn't needed for hardware multiboxing of course.