So, I'm not using Gamestudio anymore, but I find CSG brushes (= blocks) to be very useful to block out rough level geometry and layouts that are then later detailed and/or partially or completely replaced with models.
The lack of something similiar in Unity was always a bit iffy and the popularity of addons that provide such features for Unity shows that a lot of people like CSG geometry.
Unreal also has them and Epic Games uses them for example to rough out maps for the upcoming Unreal Tournament.