The reason 'gaffers tape' exists, is that duct tape works too well in some cases. In stage work (where 'gaffers' labor), you want to be able to set up scenery, attach lights, etc., and REMOVE them without sticky residue that duct tape often leaves.

My goodwife, Ferrara, and I do craft shows in which we must sometimes run electrical cords across an asile. We use some cheap carpets which we must tape down, but duct tape sticks so well, it will pull the threads out of the carpet used alone.....so...gaffer's tape.