is there a meaningful performance decrease on large builds?
There shouldn't be. All it does is parent into when a brick is planted (regular planted, not load-planted), painted, or wrench events sent on it and store the client of said action onto the brick object. Doing /le simply displays this value.
Currently the value does not save, so if you were to restart the server or even just save the bricks, clear them, and then reload them the last editor value is no longer on them.