yeah, if you were doing it professionally you would kind of have to. unless the customer requested you not to. I went to a repair chain once and they would not leave the rotors as is, so I went to an independent shop who would, at my request. that was back when I could afford to have brakes done. I think it cost me 40 bucks to change the pads at that small tire shop.
OK4450, I had one of those ventilated rotors collapse on me many years ago. The vanes were rusted out but the rest of it was surprisingly in pretty good shape. Never gave any warning. It was nowhere near as bad as the one you described but when the chunk collapsed, it tore up the pad pretty good and essentially locked up that one wheel. I can’t even imagine trying to drive it in that condition. What goes through some people’s minds??
When a brake job returns and requires even pulling the wheels and inspecting the work the job turns from profit to loss. Yes, on a considerable number of brake jobs that I have done the rotors looked acceptable but if I chose not to turn them and billed the customer for just pad replacement then in a few weeks the brakes were pulsing or getting noisy the customer would expect me to take care of the complaint immediately and for free.
As far as grooved rotors go, the grooves tend to have runout which makes for less contact. A groove from wear will not always be worn to a uniform depth. My brakes worked a lot smoother when I had them resurfaced. So did the brake pedal!
only if the rotor is warped as well, will the groove have u run out I think. a warped rotor I would replace. and I am talking about big honkin 1975 ford pickup rotors too. todays rotors on many cars would probably warp if similarly damaged.