AKA,
I'm inherently lazy, so I'll copy and paste the relevant paragraphs from the NG Flight Crew Training Manual...
Autothrottle Use
Autothrottle use is recommended during takeoff and climb in either automatic or manual flight. During all other phases of flight, autothrottle use is recommended only when the autopilot is engaged.
Autothrottle ARM Mode
The autothrottle ARM mode is normally not recommended because its function can be confusing. The primary feature the autothrottle ARM mode provides is minimum speed protection in the event the airplane slows to minimum maneuvering speed. Other features normally associated with the autothrottle, such as gust protection, are not provided.
So, in answer to your question, A/T Arm mode will protect against slowing to the Minimum Manoeuvreing Speed (i.e. Stall). The Minimum Maneuvering Speed is the top of the amber bar on the speedtape, which approximates to the stall speed at 1.3g.
Cheers,
PA28
P.S. Sorry saints44, we appear to have thoroughly hi-jacked your thread!