Advanced Output actually doesn't use much resources at all.
During a show, trying to juggle layer transform controls would be the worst thing you could try to do, especially if the wrong layer is selected by accident (happens a lot).
One of the reasons Slice Transform was built was to make on the fly mapping during performances so fast and easy. There is a reason there has been a 7+ year record of responses on this thread saying "leave the mapping to Advanced Output and Not in your layer". Things go bad really quickly. It's a Lot easier to assign a slice transform to a layer and do your editing in real time in Advanced Output. Everything is nice and organized and is easy to find and edit. You can also create multiple looks or slices and cycle through them for various mappings and looks with a quick press of a MIDI button which is super handy for getting creative with your mappings during the show.
Here is a short video showing how to do this:
https://vimeo.com/485138882
Also, Do people actually do "prepared VJ sets"? I've never seen this happen once in over a decade of working in this industry.