The "point" to me was as the designer/main engineer of the AA-12 stated; to provide US troops or sworn LE officers with a full auto weapon in MOUT(urban areas) or as a man portable weapon to defend positions or remove IEDs/ambush set-ups.
His goal was to improve the big M-16 looking 12ga; as used by action hero Steven Seagal in the 1990s film: On Deadly Ground,
www.IMFdb.org . I don't recall the full name of the older 12ga but it was flawed/unused.
The main problem with the AA12 is it's large size & weight.
As a US Army veteran in a combat support unit, I can tell you size, weight, ammunition, tools-spare parts etc can be a serious pain if a large weapon is issued. I never liked the older type Mk 19 40mm full auto weapon either for many of the same reasons.
A better 12ga spec ops or LE shotgun would be the type from
www.PennArms.com . They sell cool 37/40mm weapons too.
The old Discovery or TLC channel had a series called Future Weapons. They did a in depth look at the AA12 12ga weapon. It may still be online or on YouTube.
ClydeFrog