More friction = better grip and hold. And also, it does help with water shedding. It wears down ultra soft pads quickly e.g zoo! koxx yellows etc. If your concerned about pad wear then get harder pads. Smooth rims with tar can make the pads 'stick' and this causes loss of power from static moves if they dont come unstuck too well. Also, any slight bit of moisture and a smooth rim will provide a crap holding brake where as a grind will more or less perform the same, given it has good pads working on it.