One of the reasons i use the AT ARM mode on the 737.
Some would argue it is not really a satisfactory or logical reason to go against the Boeing 737 FCTM recommendation that the AT should be off if conducting a manual flying (as against autoland) approach and landing.
If the F/O ignores your initial warning of unstable approach then simply take over control and if a GA in needed it is quite easy to push open the thrust levers manually.
