I use very few functions to keep things as simple as possible for operators. All my engines have ESU decoders. All steam locos have sound; 2/3 of my diesels have sound. The rest are LokPilot non-sound.
F0 = headlight only, and I have it set to dim automatically when the engine is stopped or in reverse.
F1 = bell
F2 = horn/whistle
F3 = rear light
F4 = Mars or Gyralight, for engines so equipped (e.g., PA-1's, Berkshires with operating Mars lights)
F8 = sound on/off
That's it. I occasionally play around myself with Drive Hold, Run8 and Coast, which I map to F5-F7. But I don't use these for op session engines. KISS method is best for operations, IMHO.
John C.