I say a niche tool because I've never really understood why someone would prefer a Window Manager that places a lot of constraints than one that lets you controls / customize the windows as you please and is thus "freer".
I guess it can seem useful for, say, multiple terminal windows. But would suck for a scenario where you have to open different kinds of applications like a browser, file manager, video converter, movie player, terminal etc. etc. (just citing all the apps I have open now and am multi-tasking with) where the ability to stack them would prove to be more productive for the user.
That even control freaks like Apple, who like to think only they know what's best for their consumers, doesn't use a tiling only WM in their OS is telling. Even Microsoft switched from a tiling WM from Windows 2.0 on wards and has stuck to it (Source: https://en.wikipedia.org/wiki/Tiling_window_manager ).