From the standpoint of application, yes, it sometimes represents a grab, pull, or some other such technique.
However, it is also done for purposes of adhering to one of the laws of physics; ie., for every action, there is an equal and opposite reaction. Thus, the harder the retracting fist is pulled back, the harder the punch is fired, and vice-versa.
As an experiment, try this...
Start with both fists chambered on the hips. Throw one punch and don't do anything at all with the other fist. Feel the power.
Now try it beginning with one arm extended and pull back the non-punching fist to the chambering position forcefully. You'll feel a real difference in the power of your thrust.