Exactly as described, this is a simple on/off switch enabling the frame loss sub-test as part of this profile's overall test run. Because the frame loss test's own starting-bandwidth setting can reference the throughput test's own measured result, enabling frame loss without also enabling throughput would force that starting-bandwidth choice to effectively fall back to the profile's flat configured bandwidth instead, since there'd be no throughput result to build on. For example, a profile with FrameLossStartBw set to maximumThroughput but ThroughputTest disabled would have no actual measured throughput value to start from for the frameloss test that runs.