idle switch purpose/why no overrun cutoff on AT??? -- Audi 5kT

[Ameer Antar]

Would there be any benefit/loss from using the overrun cutoff switch and ecu
from a manual trannied car on a car w/ AT? From the manual it says it cuts
off fuel if the car is warm, the throttle is closed and, and the rpm is
above 1500. Why would this not work w/ an AT? It seems it would benfit by
not using any fuel during decel. Also, what is the idle switch input used
for in the ECU. It seems it would help for the overrun cutoff switch, but
what do the AT cars originally use it for? Thanks in advance.

-ameer