Coordination is desirable in all cases. It is mandatory in some jurisdictions but not always achievable. For example fuses over breakers are always troublesome due to very fast trip times at high fault currents on fuses.
With small circuit breakers on solidly grounded systems standard overcurrent protection can do double duty and coordinates well. As sizes increase generally speaking ground faults become much smaller than phase overcurrent and so phase overcurrent ceases to provide adequate protection. For instance if your ground fault path has an impedance of 1 ohm on a 480/277 system the theoretical maximum ground fault is 277 A. For example a 100 A MCCB on a B or C curve might not trip for a minute on ground fault, while we can agree 100 A isn’t very large, and a 400 A breaker will never trip.1 ohm is considered pretty low in many grounding standards. Hence the reason NEC pushes for ground fault protection in the first place.
If you run high resistance grounds by design ground faults are well under 100 A and typically 10-30 A. At this range a 15 A breaker probably won’t trip. Ground fault relaying is mandatory. So coordination might be a consideration with small breakers but most of the time you can ignore phase/ground fault coordination,
Coordination on ground fault relaying between relays is nearly always done using time delays. On high resistance for instance a motor starter might be set to 0-1 second, a feeder at 2-3 seconds, and a main at 4 seconds. In low resistance systems the resistor is often sized for 10 seconds so this is also adequate. In solidly grounded systems though like phase overcurrent you want to aim for 350 ms between levels using the standard from the old electro mechanical days and coordinate even faster if practical to do so (think arc flash) to minimize hazards and damage. Many ground fault relays are also strictly definite time (not time-current curves) so timing is much simpler than having to worry about tap/time dial/curve shape.
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