I have mine setup like that too. Simply put, most of the time I don't need a second monitor, and when I do, it's for quick glances, nothing major. Vertically stacked monitors reduces the space occupied + how much you need to move you head to look at the second one, so it's a win win for me.
To be completely honest, with a most things you don't really need more than 1 monitor, just buy a mouse with lots of keys like the g600, create some macros (maybe add a productivity app or two) and you will never need that extra or multiple extra monitors.
I have a bunch of HDMI switches, so the way my setup actually works is my bottom monitor is reserved for me main PC and gaming consoles, and the top monitor is reseved for my main PC (2nd monitor), my secondary computer (surface pro 7 fanless - really good since you can completely close it and use it as a very lightweight fanless PC), which runs automated tasks and such, and lastly my tablet, which displays all my emails, weather, news, alarms, play music out loud etc all on the same screen. (to fully achieve proper screen mirroring you need an app called Second Screen on Android to force whatever resolution you want so that the display is completely filled).
Most of the time, my bottom monitor is reserved for my main PC, and the top one is reserved for my tablet so I can see and instantly react to everything that's happening.
My monitors are 24 inches (I wouldn't go any bigger for any multi-monitor setup)
Also, my bottom monitor is connected to an arm, which allows it be sitting directly on the desk. The top monitor is connected to one of those tall monitor stands that i bought off amazon.
So there is my explanation...
{also, of course with all these HDMI switches, I have a bunch of keyboard and mouse switches - the same keyboard and mouse can be used on everything (yes even the gaming consoles). For the tablet I don't have them connected, instead there is a second mouse using Bluetooth for connectivity - this way I don't have to switch input if I have to use my tablet}