When having cantilevers it's important to check the pads and also the cables.
Pads: depending on quality, weight and km, those will last more or less kilometres. All of them has a maximum wear. It's important to change them before that maximum arrive if we don't want to damage the rim of the wheel and, of course, for security reasons.
Cable: when using the brake we use the cable all the time, it's normal that with the use the cable gets longer, we can adjust the cable a couple of times, then it will always need to be changed for security reasons, since the brake can broke blocking any chance to use our brakes.
It is also important to clean , every now and then, the spring located on each side of the cantilever to ensure their perfect function, we will do this with our bio cleaner and the water pressure machine.
Here it is an example of a new pad vs a over used pad (it has damaged the wheel).