I have an add on logger box (IOx,
I/O Extender Board v1.0 for M2/Extra) that adds 8 ADC channels as well as 8 separate EGT channels, a 3-axis accelerometer, and a GPS for logging. This allows CAN pass through logging of my accessory sensors and accelerometer with my laptop (GPS not supported yet). The MS3 and MS3X combination has a total of 6 ADC channels for extra sensors outside of the dedicated sensors for normal EFI function (manifold pressure (MAP), crank/cam trigger (VR or Hall effect), intake air temperature (MAT), coolant temperature (CLT), and throttle position sensor (TPS)).
I don't think you would want to use the MS3 purely for logging purposes but that adding all of those sensors, you are 90% of the way to EFI.