Their primary purpose is detecting cloaked and subterranean units and buildings, as well as approaching enemy units. In order to be used, the MSA has to be deployed. This is necessary because the highly sensitive microphones and scanner arrays are otherwise distracted by the vehicles' own vibration and motor noise.
Since Nod has monopoly on the two aforementioned technologies, they are only of practical value during the GDI campaign, albeit still available to Slavik's unnamed commander. However, when CABAL went rogue during the Firestorm crisis, Nod used them extensively against CABAL's stealth and subterreanean units.
This unit was essential for detecting stealth and especially subterranean units.