With the PET (polyester) adhesive, resistant up to 250°C, you improve the adhesion of your print to the heating plate. Thicker than kapton, it applies more easily leaving less bubble, as well as better grip for ABS. Leaving no adhesive residue when removed, PET will become your new default adhesive for any print that requires a heated tray.
PET is a polyester tape (PET + silicone).
The advantage of putting small strip: applies more easily, and only the damaged or worn strip is changed.