I'm a doctor, not a mechanic
Note: Read about how to delete brushes on Actor Overview.
In UT2003, it doesn't matter much if you brush delete because static meshes cure that file-size problem.
- Reduced filesize. (Usually not much if the map is compressed.)
- Hides secret tricks such as Jailbreak escape routes, although people will usually rather use "ghost" to figure them out than open your map in UnrealEd anyway.
- Superficially hides "l33t brushwork so it can't be nicked." See below for how to reveal it anyway.
- Brushwork can still be revealed and copied. Since the BSP is still present, you can simply intersect (which defeats all "security considerations").
- Commonly considered antisocial in the Unreal community. (Those who just want to steal geometry still can, but those who honestly want to learn from your skills can't.)
- Crashes when you try to select the brush that belonged to the deleted brushes surfaces (Shift-Click on surface).
Bot 40: I always delete(d) my brushes in maps just to keep the filesize down. I'm on a 56Ghey so it takes a long time to upload as well as download ya know :-) I always keep a copy of the map with brushes on my HD and put a note in the readme so anyone who wants to look at the brushes can if they want.