Fuses may not protect down stream equipment, but then again they might.
You can never assume that a protective device, like a fuse, will protect another protective protective device, like a circuit breaker. Fuse-breaker and breaker-breaker combinations require actual testing.
You should never use the 'current limiting' effect of protective devices when performing short circuit calculations for equipment locations.
Let-through currents maybe used when considering the protection of specific non-active equipment (i.e. cables, switches, transformers, and electronics).
