Anywhere there will be people with Secret Service protection will have them there way before and sometimes after the event. They are part of every aspect from catering, setting up of electrical to decorations. They check sight lines of visual obstacles, ability to move quickly and a host of other things that don't come to mind right away. They will be there hours and hours before the event checking what/who comes in, etc.
Of the times I had to work with them (military) they were omnipresent and we were all White House Security cleared individuals. They were still all up in it. I have to admit that they have their **** together.