The masking tape is used as Estes instructed to secure the motors. I prefer placing tape on the motor tube in the traditional method because it allows tweaking and testing the friction as the motor is pushed inside the tube, and it also does not leave sticky residue on the tube finish when it is removed.  Also, when the tape is burned (and I don't see how it would not be burned), it leaves a very sticky burned scum on the motor tube. (see next photo)