If you have a pulsation on stopping the rotors are warped. They will need to be checked with a micrometer to determine if they can be resurfaced of discarded. The government set the regulations.
There will be a pulsating on braking.
There is a pulsating on braking.
Yep.
Grinding
could be bad rotors, or brake pads wearing unevenly, which would result in bad rotors.
We need to know the year, make, model and front or rear rotors to answer that one. also need to know if the rotors and hubs are one piece or separate.
Bad rotors
There can be. Only way to know is have your brakes and rotors inspected.
No just the bad one.
what do brakes look like when they go bad, how far can rotors go?
You do not rotate rotors. Replace a bad rotor or have it machined if possible. Never rotate them to another wheel location.
bad brake rotors or alignment shocks struts