It clears your trays, you have to rechoose and reslot every single power. The UI is outdated(that's a nice way of saying terrible) and inefficient. Everything about the experience sucks, the exception being the ability to type /respec to start one.
What would be ideal is granular control. Drag and drop power order(staying within the proper leveling rules of course), remove as few or as many slots as you want instead being forced to do every single one, etc.