In order to be used the MSA it had to be deployed. This was necessary because the highly sensitive microphones and scanner arrays 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. They were replaced with better sensors, based on lighter, combat-worthy scouting units.