I use the GAD 27 for flap control (presets), trim mixing (inputs from either stick), trim speed control (finer adjustments in cruise than in landing and takeoff), and light dimming. Lighting inputs to the GAD (up to 3) are potentiometers that simply vary an input voltage - I used 10k pots. Each pot controls a lighting circuit (up to 3) and each circuit has 2 outputs - one is DC voltage and the second is PWM (pulse width modulation) for LED control - thus a total of 6 possible output circuits. Garmin screens (G3X and GTN) use DC voltage input for lighting control while LEDs (typically in buttons, switches and lighting strips) behave better with PWM.
I used all three input circuits (3 pots for input) with one for screens, second for switches and buttons (including buttons on devices), third for an LED strip for panel splash lighting (either red or white). GAD 27 allow different profiles (voltage to brightness conversion, and cutoffs) for all 6 output channels. GTN also allows different profiles.
More control than you can ask for, but I really like the results night flying.