I’ve just setup Workspaces on my Haiku system and wondering if someone is using this application ?
Most of the time, it’s the opposite : you have several screens and the system is using these various devices.
Workspaces is the opposite : you only have one screen and want to use virtual desktops by switch from one to another.
The Workspaces replicant has been embedded beside my Deskbar since BeOS, so about 25 years now. I use it daily, every time I need to change between 4 workspaces whenever I have the hand on the mouse. If not, I use CRTL+ALT+CursorLeft/Right.
Very often I use the replicant to drag a window over to/from another workspace.
I never had more than one monitor at home. The past ~15 years that was the panel of a notebook.
Every single day.
BTW most Linux desktops have virtual workspaces built in. MacOS has them, even if they are a little trickier to work with. It’s only Windows that resists them.
IIRC I think that windows also has them (but I never used them, I rarely use Windows)
EDIT:
It’s called “virtual desktops”: Multiple desktops in Windows - Microsoft Support
I had a look myself. Apparently this emerged in Windows 10. Which would explain my ignorance, I haven’t used Windows since version 7!
They are always very late: they added tabs in the file explorer in Windows 11 (it exists since years in GNOME) 
Windows has had virtual workspaces before. But you had to download a tool for this Desktops - Sysinternals | Microsoft Learn
To answer your question; I am using this functionality all the time. But I mostly don’t use the workspaces applet, only having it as an indicator. I usually use alt-F(1-4) for 4 virtual desktops. Sometimes more but usually 4 is enough
I belong to the opposite faction, I almost never use them even on MacOS where I prefer Mission Control (or the good old Exposé).
Actually, I wish we had something similar for Haiku because the workspace concept does not fit my workflow.
Windows has supported creating and switching between virtual desktops since NT 3.51 (*actually from NT 3.5) and that predates BeOS. The API (CreateDesktop, OpenDesktop, SwitchDesktop) was fully functional but it was just not exposed to the user via the OS interface. There were a few apps that allowed to utilize the functionality, and I remember using one of those on NT 4 and 2000 (that was before Sysinternals released the Desktops tool). But the API does have limitations as it was designed with security in mind, and not for the great UX (who would expect great UX from Microsoft anyway?), the biggest of which is the lack of ability to move windows across desktops. That’s why in the Windows 10 virtual desktops feature, no new desktop objects are ever created, and the OS just manipulates the visibility of windows.
And now for the funniest part, the Microsoft’s patent from 2003 for a Virtual desktop manager: United States Patent Application: 0030189597 .
User here also, and as @humdinger mentioned next to the Deskbar at the top of the screen, mostly they are setup up to 8 or 10 Workspaces.