In order to be used the MSA had to be deployed. This was necessary because the highly sensible microphones were otherwise distracted by the vehicles own vibration and motor noise.
Nod commanders on the other hand used the MSA to detect either enemy Nod commanders, mostly during the Nod Civil War. In addition to that, Limpet Drones could be uncovered and destroyed to prevent infiltration.
This vehicle related article is a stub; you can help the EVA database by expanding it.