Bullet Physics, when to choose which DynamicsWorld?

Question

I have a few general questions about the bullet physics library.

Here is my real understanding in a nutshell:
btDiscreteDynamicsWorld - The simplest world of physics, processes only rigid bodies, may have better performance.
btSoftRigidDynamicsWorld - the only physics world that can work with large jelly molds | btContinuousDynamicsWorld . If you have really fast objects, this will prevent them from drawing each other or flying through each other, but otherwise it's like btDiscreteDynamicsWorld.

Is my understanding of the btDiscreetDynamicsWorld, btContinuousDynamicsWorld and btSoftRigidDynamicsWorld classes correct in terms of functionality, purpose, and performance?

Why does the user guide recommend the btDiscreteDynamicsWorld class?

btSoftRigidDynamicsWorld is the only world that can handle soft bodies, so what if we want to integrate continuous physics and soft bodies?

How fast is it fast enough to consider using btContinuousDynamicsWorld, and what are the disadvantages of using it?

Edit: My Buddy Mako also posted this question on the Bullet forums: http://www.bulletphysics.org/Bullet/phpBB3/viewtopic.php?f=9&t=4863

Answer 1

, btContinuousDynamicsWorld, ( ).

, btSoftRigidDynamicsWorld, btDiscreteDynamicsWorld.