Brush entities can cause leaks, actually. It's all about their origin, or center if you want to call it that. Same goes for point-based entities: whenever their center is in the void, they cause a leak.
Combining multiple brushes into one entity has some drawbacks bytheway:
- whenever a part of it is visible, all parts are rendered
- it's hard for the compile tools to determine when the entity is visible, and when not. Entities that span across multiple leafs could even always get rendered... this has to do with the way the map is cut up into a bsp-tree.