As pointed out by everyone, we have a problem at the starting point with nomenclature. There are a few “boots” that could be observed during a brake job. A torn caliper piston boot should have been an add on to the brake job. If it wasn’t, either take care of it soon or leave it to your next brake service when you can expect to have the caliper rebuilt or replaced. A torn caliper pin boot shields a slide pin that the caliper slides on everytime the brakes are applied. It is not unusual for damage to these to go unnoticed. Eventually road grime will prevent the caliper from sliding on the pin and either the brake will become less effective or will not retract and continue to contact the brake rotor. Finally, he could have referred to the axle CV boot. With a torn axle boot road grime gets into the CV joint and will start causing a grinding noise especially when steering. If it hasn’t been too long these can be repaired in place with a two part boot. If it’s been long enough to allow grit to get into the joint, you can wait until symptoms arise but it will mean replacing the joint. These days it is cheaper just to replace the axle.