I don't live in a place where a folder is the optimal bike -- semi-rural, own house with extra room, full size bikes make sense -- but I have a commute for which a FB is extremely useful.
Bike-bus-bike commute: currently, I have a bike locked on one end of the commute and ride another one to the station because it's winter and no one makes 18" studded tires for my Birdy. Drivers don't like tossing full-size bikes into cargo and bikes get bumped for luggage if needed per bus policy. Outside of snow/ice weather, I much prefer taking the folder with me on the bus. If I thought I'd stick around for another winter, I'd be looking to trade the Birdy for a folder with 20" wheels.
Now that I have a folder, I'm finding uses and convenience I would not have imagined. Takes up less space at home, unfolded, and disappears folded. Fits easier into the car unfolded; folded, it will fit in a trunk with the seats up. Recently, I took it cross country by plane in checked luggage--much better experience than renting at destination. Comes with me in the shopping cart at the grocery store. I will sometimes visit the city (Boston), using the same bus service I do for commuting, and all the same reasons a folder is so great for commuting by bus apply to travel for leisure.
So, if pressed, I'd say where I live is best for riding a folding bike because I'm easy folding biking distance (5 mi) from a local, commuter bus line, which can be the first leg in taking me and my folding bike anywhere in the world...