right, the TV is letterboxing. This means that it saves a lot of energy not having to light those pixels and also, being a 50" TV, it is like having two 1920x1080p screens side by side (3840p).
Sorry if I didn't explain myself correctly. It is letterboxing, sure, but what I mean, the TV becomes an ultrawide display, with its own sound, and with enough space for displaying the equivalent to two displays at the same time, instead of the "Extend these displays" feature. It's much simpler, you just split the windows in two.
I will be honest, that's a beyond price feature. Many people want a 4K screen, but those who want an ultrawide display, are also many. With a Samsung TV with a feature like this, you get 2 displays in one when it comes to productivity and the good things of ultrawide gaming, plus native 4K if you need to -for certain productivity tasks, or for games that don't support ultrawide-.
When in game you just see 16:9 4K or ultrawide 32:9, but in the desktop it looks like this;
Two browsers side by side, 175% scaling:
Same at 100% scaling: