Parisien, Enzo
Good morning..... Once new pads have been fitted it takes a few miles for them to 'bed in'. Effectively this means that after a very short period of time the surface of the pads will form a mechanical fit to the disc, rather like pieces of a jig-saw. Once this has been achieved the full surface area of the pads will offer maximum retarding effect. It follows that the developing shape or pattern of both the pads and the disc will be unique. Suppose that these pads have plenty of friction lining remaining but they have had a hard life and you remove them and then fit them to the caliper of another car. The mating surfaces of pads and disc will not align perfectly with 'peaks and troughs'. The brake will not therefore necessarily operate at best efficiency. Furthermore the braking effect may not be even and result in pulling to one side, especially under load. There could also be squealing. As one would expect these symptoms will not occur in every case but it is nonetheless worthy of consideration.
Regards,
Paul