If you press the Auto-throttle speed button, auto-throttle speed mode is de-selected and it falls into 'Arm'. This means you have manual thrust control back but auto-ga thrust capability if you hit toga and low speed protection if you get too slow. I thinks its a good way to do manual flight but there are drawbacks. If it is gusty, the low speed protection can keep kicking in which is annoying. Also, I heard a story that a crew once upon a time got too slow in the flare and the low speed protection kicked in causing a tail-strike (with the pitch up moment). I can't see this myself but who knows. When I close the throttles, I hold them closed to avoid such occurences. Hope this helps.