In fact, some manufacturers recommend simply replacing the brake pads themselves without resurfacing or replacing the rotors, as long as the rotors measure more than the minimum thickness and they spin true (are not warped). That would mean your first brake job or two could possibly include brake pads alone.
Most of the auto-repair shops and mechanics would suggest you change the rotors when you change your brake pads. All types of cars have rotors and to change all four of them can be quite expensive and not everyone can afford to do it frequently. Rotors generally have to be replaced after 15000 – 70000 miles.
This can cause the rotor to warp or break. Second, the lack of brake pads means the heat from the friction won't disperse correctly, which could cause the whole braking system to overheat and fail. It can cost up to $289 to resurface the rotors and up to $485 if you replace the brake pads at the same time.
The average brake pad replacement cost is $150 per axle, and can range from $100 per axle up to $300 per axle. There are a few other pieces of hardware that are found in the brake system which might need to be serviced as well, including calipers and rotors, but the most common service will be to replace brake pads.
If you're doing a lot of braking it will wear down faster. My guess is no, typically rotors can be resurfaced, made smooth, aka grooves removed, when new brake pads are installed. If you installed new rotors, the old pads will have grooves from the old rotors.