Naw, it's a good idea. In fact the less airspace you have in the freezer the more efficiently it runs so you may want to leave the water jugs in there all the time to save on electricity.
You can also turn the t-stat on it down to the lowest setting, and do the same for any other refrigerator/freezer in the house. The colder it is to start out, the longer it will take food to thaw.