For me it is very simple. All buttons and the two rocker switches are linked with vJoy and FSUIPC for the PMDG737-800 and
for X-PLANE ZIBO to the X-PLANE vJoy button set-up.
I have a CP-Flight 737 MCP wich i can use fore PMDG and X-PLANE.
Only the left hand button (1) is for AP disconnect and the R/H (back side)is for start/stop clock
The L/H rocker switch is only for trim up/dwn.
What else needs to be activated goes to my CFY Throttle Quadrant or directly to my CP-flight Nav/Com panels.
This only for both 737-800
Other aircraft other configuration
Add info: Trim function is performed by the CFY TQ software. Also the throttle/reverser levers, spoiler speedbrake/flaps, parking brake, etc.