For information about BSP and ABT rendering, see:
http://manual.conitec.net/culling.htmBSP is by far the best scene management system for hardware accelerated systems, which is why it's often used today by commercial high-end engines. Contrary to rumors, it's also good for outdoor levels when they contain buildings.
However, hardware today is so fast that you don't need a BSP renderer anymore for small or medium sized indoor levels. You can also render them with more primitive systems like ABT or even the old-fashioned Octree. For 90% of all Gamestudio games, the A6 BSP renderer is not faster than the A7 ABT renderer. That's why we moved BSP to the Pro Edition in exchange for physics.
There are also marketing reasons. Many newbies don't understand the limitations of a BSP renderer (like lengthy precalculation and convex geometry for the PVS process). Thus, we'll get rid of all those limits in the A7 lower editions. Someone who upgrades to Pro will likely understand the Pros and Cons of BSB vs. ABT, but we can not expect this from newcomers. From its very nature, BSP is a Pro feature.
