What is the use of heat shrinkable tubing with adhesive layer? In what cases can a tube without an adhesive layer be used?

The adhesive layer works for leak-proof sealing of the connection. When heated the tube shrinks and the adhesive layer melts and spreads inside for perfect adhesion. Surplus of glue goes outside the tube and forms a sealing along its edges. So if you have special requirements for leak-proof connection, it is better to choose a tubing with an adhesive layer. Moreover, this kind of tubes have a higher shrinkage ratio (3:1, 4:1, 6:1) in comparison with a standard ration (2:1), and thicker walls for voltage up to 1 kV.