Well, if you have a real fine single-stage trigger, the stainless lower is not going to get it's pin-holes (hammer and trigger) hammered out like the aluminum ones. I have had my own single-stage trigger in my ss lower as long as I've owned it, and have yet to have to re-time the trigger. That's more than I can say for any of the forged AL receivers I have owned or worked on.
Not saying that it is worth purchasing a ss lower for that alone, just that it is one of the advantages.