Brake Shoes

The groove in the lining is designed to cool the pads. Obviously brakes cause wear, as that is how friction material works. As the drum wears, it will only wear where there is contact, thus the raised ridge in your drum. This means nothing. You turn them smooth again. And as they wear with more miles, the ridge will raise again. Not a big deal, just normal wear. I have seen thousands of cars like that. I am not convinced the groove does anything, but then I haven't spent tons of money on research and development.