i think you are talking about level construction, ways to speed up the result:
-use fewest brushes possible(not sure about this). if you have an object with a few brushes, move it out in the middle of nowhere, put a brush around it and intersect. This will make it one brush
-you can use the 2D shape editor, but you will notice the ends of the extruded brush/revovled brush have a lot of wasted polys in them. Add/Subtract the brush, select the polys on the end of the brush, and set the same texture and do align->align to wall or floor/ceiling. Then polygons->merge on the brush and rebuild.
-some people claim that semi/non solids improve poly/node count, but i noticed it increased in my level, so i am not sure about this.
-the cut function, i think you mean intersect/deintersect, they can help prevent bsp holes, but i am not sure about performance.
As for non-geometry ways to improve performance, use as few dynamic lights as possible, keep meshes(wepons, ammo, pickups...) in low poly areas and inside in outdoor levels.