Carry-over cooking refers to the phenomenon that food retains heat and continues to cook even after being removed from the source of heat.
The larger and denser the object being heated, the greater the degree of carry-over cooking. This holds true for pressure-cooking. That is why when the whistles are over we need to remove the cooker from the source of heat so that the heat built up inside the cooker continues to cook for a short while and then as the cooker cools, the pressure can be released.
Even while baking the carry-over cooking applies. Often after being removed from the oven the internal temperature in the baked food be maintained for some minutes.
This also holds true when we steam idlis and dhoklas. It is not advisable to cut the dhokla as soon as it off the fire. We allow it to rest for a few minutes so that we get neat even edged pieces.