You may have 2 monitors and want to have different views on each monitor.

You cannot actually separate the views completely, but you do not need to.

You just stretch the window for the app right out across the two screens, then split the window and position so the split is exactly on the join between the windows.

Then one pane is on one monitor and the other on the other, and they will stay like that as long as you leave them that way.

Meanwhile you can now make one 3D and the other plan or whatever.