straight from the maya docs:
"Baking a simulation allows you to generate a single animation curve for an object whose actions are being provided by simulation rather than by keys and animation curves (keysets). Many types of animation in Maya are not represented by, and therefore not available for, keyset editing. Examples include objects animated with inverse kinematics, by expressions, or along motion paths.
Baking a simulation is useful when you want to edit a single animation curve instead of all the contributing attributes that affect the behavior of a single attribute. Examples: an object affected by a driven key or an expression."