Sure, I work from office and home part of the day.
Because I have 2 or 3 ext. monitors I do NOT need virtual desktop/spaces most of the time. I only use macos spaces feature when I have NO external monitors during travel (of course, many people use spaces AND external monitor especially if they have 1 setup... but for me it's a hassle to delete/add macos spaces each time I move from work/home because Mac doesn't remember them per display).
Anyway, each monitor has only 1 space per display in my case:
Work:
[Macbook screen] [ Ext. Monitor 1] [ Ext. Monitor 2]
Home:
[Macbook screen] [ Ext. Monitor]
With Rectangle, I can snapshot window layout across All Displays and treat them as one entity. This makes it easy for me to switch between home and work layouts. I don't think Rectangle handles macos spaces, it just looks at what's showing on each display.
With your Tangrid Workspaces feature, I believe I would have to create new workspace for each display individually. Yes, you are right, I will only need to do this once, not every time. That part is NOT the hassle.
But now when I go to work for example, I have to click on Tangrid slideout for my "Work Macbook" workspace, wait, then click on "Work Ext. Monitor 1" workspace, wait, then click on "Work Ext. Monitor 2" workspace. And when I go home I have to click on "Home Macbook" workspace, wait, then click on "Home Ext. Monitor".
This is definitely a first world problem :P But in Rectangle I just switch from "Home" layout to "Work" layout and windows move to the right display (again I don't really use spaces). My script quits Tangrid, derives setup from connected monitor, uses Rectangle to move windows instantly to the right spot, then Tangrid starts and groups by proximity.
I do use your workspace feature when there is no external monitor.
Sorry I should've been more clear, it's not just saving across all displays that would be helpful, but activating workspaces across all displays in 1 click.