I'm planning on building a simple system with a microcontroller to turn a camera on, take a picture, and turn the camera off (perhaps some added functionality too). I was planning on using low side FETs to control the camera functions, but now I'm wondering if I should be using like a optocoupler to isolate the camera from the arduino. If the camera and Arduino are powered from different batteries the grounds will be connected. I guess I'm really wondering, why or why would I want to use an optocoupler in this type of situation?