"Simulate Block Transfer" (which is now enabled by default in the latest dev builds) is a technique used to properly emulate certain functionality present in some games. It was developed as a lightweight alternative to the performance crushing "Read Framebuffers to Memory" rendering modes, but still incurs a minor performance penalty as compared to plain ol' buffered rendering.
Examples of games that require this option enabled include The 3rd Birthday (missing text/dialogue boxes), Ys Seven (minimap functionality) and Soul Calibur (Screenshot taking functionality during custom character creation mode). Previously, those goes games required one of the two "Read Framebuffers to Memory" modes if order to be emulated accurately.
Fast Memory can be enabled globally now but it's mainly a performance booster. If you have a decent rig you can keep it off. Same applies to Multithreaded, Mipmapping and Vertex Cache. I actually recommend keeping them all off if performance is not an issue for you.
Blood Boal, we can continue the discussion in the
PPSSPP OT if you wish, we rapidly heading offtopic here lol.