As you are indicating, this is a design consideration which will usually be very case specific.
In your example, it appears you are refering to nontime delay fuses. In this case, it is likely higher ratings will be need due to the short time/trip curves provide by this type of overcurrent devices. Perhaps another type is more suitable such as your standard inverse time circuit breaker.
The bottom line is since the code gives maximum allowances, it gives designers plenty of flexibility when considering proper protection.
In your example, a 200A device and 250A device will have nearly identical trip times for short-circuits and ground-faults. However, the possibility of nusiance tripping at 200A is greater.
Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter