This feature is for pinning/favouriting tabs so they're accessible through all saved windows / workspaces.
If I've favourited tab then it's showing as pinned tab on all saved windows within this profile.
This feature already exists on Arc browser and that's prettty good feature if user uses different windows to manage his workflow.
For example: i'm using "Personal" and "Work" saved windows, and I constantly switch between them during work day. I would love to set "favourite" - "Facebook", "Discord", "Telegram" so these tabs are always showing even if I switch my saved windows.
In Arc browsers case they've "Favorite" tabs so they're at the top within the same profile. For example I use the same 2 spaces/windows "Personal" - "Work" with my personal profile and I've favorited few tabs there and they're always accessible withint these two spaces. I also use third space/window with different profile so those favorited tabs are not showing there - they're tied to profile.
Personal:

Work: 
Third space:
