Nice!
Once you start wrapping your head around the concept all sorts of possibilities begin to materialize. A person may like riding SS or FG but find the routes they want to do make a traditional set up impossible (or problematic beyond practical). A commute that is predominantly up hill one way (and down hill on the way home) is a common problem.

If one wanted to bike tour SS from Vancouver to Calgary for example it would be virtually impossible on a one ratio bike without a lot of walking. However, two ratios make it potentially doable with long stretches between swaps.

The route from Vancouver to Hope (about 180km's) can be done with road gearing, it's mostly flat. Switch to mountain gearing for the 60km climb up to Alison Pass. Road gearing from there for a couple of hundred Km's to Penticton. Same gearing through the whole Okanagan Valley to Revelstoke, about 300km's more or less. Mountain gearing over the Rogers Pass and road gearing down to Golden and beyond. Mixed gearing from there to Field. Mountain gearing up the Kicking Horse Pass and road gearing from there for 200 Km's to Calgary.

Or, like me, one could live in the middle of five downhill MTB parks that one can ride to but that also have long access climbs. If I choose to SSmtb I can either walk up or ride up.