Adhesive tape consists of two important components: the adhesive, which bonds in the form of a pressure-sensitive adhesive on the adhesive tape and is sticky throughout. And the backing (paper, film, fabric, fleece, etc.), which holds the adhesive. Now there are adhesive tapes for many different purposes. They differ in terms of speed, length and solidity of the bond.
And this is exactly where primer comes into play. It is a thin layer that is applied to the bottom of the backing and reinforces the adhesion of the adhesive. The adhesive tape bonding primer is always used if the adhesive should adhere especially strongly to the backing. This makes sense if the adhesive tape is only attached temporarily and no glue residues should remain after removing it – with masking tape, for example.
Or if adhesive tape should bond two things for ever. The increase in adhesion allows mirrors attached with adhesive tape to stick to the wall. Without the primer or adhesion bonding primer or even an anchoring aid, the adhesive might not glue strongly enough to the backing of the adhesive tape and let the mirror fall from the wall.