Modal - locks you to the functions contained in that box, until you close it. You will not be able to use anything outside functions of that box.

Like you would not be able to go bowling if you are locked in the jail cell for drunk driving (not that I had that experience)

I think the only thing you can do prior to opening F8 is bar selection, and that range of bars will show up in that Modal F8 box. But that is easy enough to do within that box as well, so not much gained.