Quote from OrnateBaboonIt would also be hugely beneficial to decompile some official maps, and look at how Valve have done it.
https://developer.valvesoftware.com/wiki/Decompiling_Maps
Generally, any brushes that are not blocking vis should be function detail. This often includes whole buildings. However, portals will only work if they are totally surrounded by world geometry.
I thought decompiling wouldn't give accurate optimization stuff. Isn't half of optimization for the compiler only?