The only experience I had where a SS prop was essential, was on a shallow bay with a sand and muck bottom. My sterndrive would dig a lot when getting on plane, running the prop thru the bottom. As such, an aluminum prop would last 1 season. A ss prop on the same boat, in the same bay, lasted forever.
The moral of the story is that, as long as I don't drag the prop thru the bottom material, the Aluminum props hold up for many seasons.
As you saw and heard from Jimmbo, bad things happen if you hit rocks. SS has the potential to bend the propshaft and/or damage the gearcase, if you hit rocks, which Al props will not do.
There are high performance aluminum props, which give nearly the performance of SS They are about 1/3 the cost of SS or less.