and what the adj rotor for?
I'm just guessing, but an adjustable rotor is usually so the end-user can fine-tune the "phasing" of the rotor, which lets you decide just where the rotor will be when the actual spark event occurs.
This is necessary because as the timing advances and retards from mechanical and vacuum advance mechanisms, the location of the rotor tip in relation to the contact in the distributor cap changes. In some cases, this change can literally push the rotor tip well past the contact point.
This is not enough to be an issue with most ignition setups, and most are perfectly fine right out of the box, but if the base setup is skewed just enough, it could lead to problems especially with ignitions capable of lots of advance. And with a finely tuned computer controlled unit, or a high-performance race engine where precise timing events can literally mean the life or death of the engine, it can be a real lifesaver.
I'm pretty sure that with most ECM controlled ignitions, you are locking out your advance mechanisms completely so the computer does all the work. In a case like that, you use the adjustable rotor to perfectly center the tip at the contact so there is no variation and no need for the spark to jump a bigger gap than needed.
Does the timing control work like TFI, continuously adj timing, because I keep reading that You still have to do timing with a light.
Here again, just assuming, but I'm pretty sure that means you set the initial base timing with the light, and the computer takes over from there. In this case, the "base" timing might actually be the maximum advance available to the computer, then it can retard from there as needed.
Or it could be a middle ground, where the computer can advance or retard from a given point. I'd bet though, that it's a maximum and the computer finds it easier to retard as needed.
Some EFI setups with particular distributors will actually have an LED light that you watch as you are rotating the distributor. When the lights come on, this is where you lock it down.
Others that know for sure can confirm or deny those reports though.
Paul