Packing tape is a very important tool when packing for a move.  Having your boxes fly open at the wrong time can lead to some very inconvenient situations.  A friend from work recently purchased a new windshield for a high end SUV, when a box he was moving in the back of his truck opened in transit and released its contents onto the roadway.  Had he used packing tape to seal the box, he could have avoided this unplanned for moving expense.