When you compile the VIS all structual brushes are used to break up what you can see. There's no sense in drawing something on the other side of a wall that you can see, no?
Make any small brushes, ie stairs, small items(brushes), detailed. Detailed brushes will not break up what you can see. Also any weird angles/shaped brushes should be detailed, as those can mess up your VIS as well. Things that would qualify as detailed would be things that would not break up your vision significantly because of small size. Highlight the brush and do 'Ctrl+Shift+D' to make it detailed. The detail brushes will be green in your 2D view.
No, Okay, lets say I drew some stairs, always use caulk on everything, after i have finished my caulked stairs, texture them, then highlight every brush on the stairs and go to make detail. It will turn green, hit escape, wolaa your done.
read blue's comments again.
"all the governments in the world are corrupt and in the hands of the Illuminati"