When a rotor causes a pulsation, the question is whether it can be machined flat again or needs replacing. Sometimes resurfacing works; often, on modern thin rotors, replacement is the better call. Here is how to decide for a warped rotor.
Most warping is thickness variation
What people call a warped rotor is usually disc thickness variation or uneven pad deposits rather than a truly bent disc - see warped rotor causes. Resurfacing (machining a thin layer off both faces) can cut a rotor flat again and cure that pulsation - if there is enough material left.
The thickness limit
Resurfacing only works if the rotor stays above its minimum (discard) thickness after cutting - see where the minimum is stamped and how to measure it. Modern rotors are made thin, so many do not have enough material to machine and must be replaced instead.
When machining does not fix it
If the rotor has true hard spots from severe overheating - see blue hot spots - resurfacing rarely gives a lasting fix, because the hardened areas wear differently and the pulsation returns. Deep scoring or cracks also mean replace, not machine.
The practical answer
Measure first. If the rotor is thick enough and only mildly warped from deposits, machining can save money - see rotor resurfacing cost. But because modern rotors are thin and often cost about the same as machining, replacing as a pair with quality pads and fresh hardware is frequently the smarter choice.