You asked for it, so here's another one of my Keyboard Maestro Macros. This one is pretty simple. You can run a Macro based on a USB device being attached or detached. I tend to keep my ScanSnap attached to my Mac via USB most of the time, but it doesn't actually register as attached until the scanner lid is lifted which makes it a perfect candidate for the USB device trigger in Keyboard Maestro. The ScanSnap has accompanying software that allows you to direct what happens with a scanned image, this software needs to be running when you're scanning. But, I don't like having applications running unnecessarily. Previously, I'd manually launch and quit the ScanSnap software when I was ready to start scanning, but I found a better way.
I setup a simple Macro to launch the ScanSnap software when the ScanSnap is connected. This is a one-step Macro triggered when a USB device with name containing "ScanSnap" is attached. When I lift the lid on my scanner, Keyboard Maestro detects the change and the software dutifully launches. I set up an almost identical Macro to quit the ScanSnap software when the scanner lid is closed simply by changing the trigger criteria to "detached" and changing to action to quit the application.
This method works when you're accessing your ScanSanp via USB. If you're accessing the ScanSnap wirelessly, you'll want the Software running in the background regularly so it will be ready to accept scans.