Windows Layouts is useful if you have more than one monitor and want to have different multi-monitor UI layouts for different purposes. I have two monitors and I don’t understand Windows Layouts so I stay away from using them.
Workspaces, above the Windows Layouts area are very useful and are the saved different arrangements of dockers that you might want to try. A variety of different workspaces are provided when you first install krita, with names like Default, Big Paint etc.
Many people make their own named workspaces as can be seen here:
Share your painting Setup!
Workspaces will store the docker arrangement of a two monitor setup because the position of floating dockers is stored as well, not just the ones that are ‘docked’ in the main window as you can see from my reply in that topic.
For Toolbars, you can arrange their icons with Settings → Configure Toolbars.
The Toolbar can only be docked at the edge of the main window and the top or bottom edge is best. Left/right edge docking looks bad because of the wide items on the toolbar.
If you try it then you’ll understand what I mean.
The toolbar internal layout can not be saved as a named arrangement. If you want it different then you have to use Settings → Configure Toolbars.