JPJP: As I'm sure you are well aware (
though for the enlightenment of others) here's what the Boeing Flight Crew Training Manual (FCTM) has to say about use of the AutoThrottle on the B737-800:
"
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 in CMD."
"
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 maneuver speed. Other features normally associated with the autothrottle, such as gust protection, are not provided."
"
Category II Operations: The autothrottles should be disconnected when the autopilot is disengaged."
"
Decision Altitude (DA(H)) or Minimum Descent Altitude (MDA(H)): Disconnect the autothrottle when disengaging the autopilot."
"
Final Approach using V/S: Disconnect the autothrottle when disengaging the autopilot.
Furthermore, the Boeing FCTM also includes numerous references to the following statement: "
Turn both F/Ds OFF, then place both F/Ds ON. This eliminates unwanted commands for both pilots and allows F/D guidance in the event of a go-around." E.g. see: Circling Approach
OR Final Approach using V/S....
Accordingly, unless one is flying an Autoland (
i.e. landing with both autopilots engaged), when you disconnect the autopilot, Boeing recommend that you should also disconnect the auto-throttle.... and for certain non-precison approach types (
if and / or when below the MDA on those approaches) also turn off, then on, your Flight Directors and wherein as
JPJP (
correctly) states above:
"On an IAN approach the FDs will guide you down to 50 feet above the runway. However, it's not good practice to rely on them since you are below MDA. PAPI, VASI or visual reference are the approved guidance below MDA;.... a difference in actual airfield QNH/Temp and VNAV Baro, may cause a difference between VGSI and the GP indication."
the point being that you can't rely on it to be correct, hence why it's classified as 'non-precision' (
unlike an ILS), and that therein the Flight Director guidance might be duff... so turn them off to avoid any ambiguity in the guidance one is following (
but have them available - in Pop-up' mode / hidden out of view unless the TOGA button is pressed - in the event that one has to go-around) !
Boeing have / had also issued a Operational Bulletin / Amendment to Part B FCOM 1 (
which presently and for the life of me I can't seem to locate... though I'll edit this post with the relevant link when I do find it) which explicitly prohibits the practice of using "Speed Off" / 'Arm' mode during an approach & landing (
apparently due to the auto-throttle - when in 'Arm' mode - being able to cause a tail-strike during a go-around from a very low height, as it can seemingly apply TOGA power 'too aggressively', and that there's also the risk that the auto-throttle might choose that very moment to fail and therein not apply the TOGA power that one is expecting, whilst one errantly uses both hands to pitch the aircraft into a climb... go figure?! 
.. ).