While I was prototyping my main location for the demo, I encountered something that might be worth checking further, especially if you use a lot of brushes in your map.
I was using multiple brushes to approximate a model for my target location. It had a lot of DCs, so I thought I'll convert it to func_static, so every face isn't counted as a model (which is typically the case with BSP vs static meshes). I did the conversion and compiled the map. When I ran it again, stats actually showed a bit higher DC count, while tris and shadow tris went down a little bit. Tried deleting all the files (.map, .cm, .proc) – no effect. There might be something wrong on my end, so I encourage you to test this on your own.
But if this is normal, then it means Convert to func_static is much less useful than I thought. There's not much of a conversion going on here. I mean, you can still do it to add noshadows 1 option for shadow optimization, but that's basically it. That means making "models" in DarkRadiant should rather be discouraged, since the engine has pretty low drawcall limit.