Automatic updating of dimensions
When you edit the model space, it's easy to adjust the dimensions in one go. But also it's easy to see if a dimension isn't updated. It's not so nice when the dimension is drawn in paperspace though.
Here is that same sample, but with the windows both stretched to be 1200 wide:
Notice that it was "easy" to stretch the red dimension while changing the window itself. Not so for the brown though: here it needs to be edited on paperspace. Not too much of a hassle if it's only this one dim, but what happens if your drawing is more substantial that just this one instance? It could be very easy to miss a dimension ... not to mention, you're doing the same task twice!
However, notice that the magenta AND the maroon dimensions have updated without needing to adjust them at all. In fact I didn't even include the magenta dimension while adjusting the window.
... next, we'll look at how these work on blocks. In particular dynamic blocks.