Tom - Manual notching can be helpful if you are trying to mimic certain things on a prototype. For example, a train coasting in notch 1 while still moving at a good clip, or at notch 8 while climbing slowly up a hill.
I have my switchers and local locomotives set up on automatic notching with load. That way I can adjust the load on the fly depending on the number of cars. All my road locomotives for through freights have manual notching. That way I can throw the notches way up when hitting hills, and drop the notches way down when coasting. And I can independently control the throttle while doing that.
-Kevin
