When you play an animation, Maya calculates dynamics each frame for all dynamic objects in the scene. The state of a dynamic object is the collection of its current attribute settings—the settings that specify its location and display characteristics. The state of a dynamic object in any frame other than the first is based on its state in the prior frame. Maya calculates dynamic effects sequentially starting at the first frame.
For example, suppose you have an emitter and you want the scene to start when the emitter has already emitted a certain amount of particles. You can play and stop the scene at the frame where you see the particles emitted, then set the current attribute values for use at the initial state. When you rewind and play, the scene starts with the particles already emitted.