[Urban]

An air defense system is like "Russian pupets" :

AA gun are use as close defense point for bigger sam unit (area sam). This weapons are really deadly for aircraft, even the mighty A10, SU25 could not really fly with big holes in the wings. On the other hand you need a really good LOS and enough time for aiming even with radar.

Shoulder sam's are not really powerful, of course a direct hit is devastating. They are used as 'mosquitos" for incoming aircraft, disturbing the pilot, force him to make evasive maneuvers (and miss the target) or worst climbing and become a prey for AA guns and area SAMs. It's a unpredictable danger for aircraft.