One of my biggest pet peeves is an AutoCAD operator that does not lock the display of a viewport in Layout (paperspace). It is very annoying when another user double-clicks the middle of a viewport to make a change in model space but zooms and changes the scale.
To prevent a user from changing the scale of a viewport use the Display Lock option in the Properties of the Viewport:
1. Select the viewport.
2. Open the Properties.
3. Scroll down to find Display Lock (default is NO)
4. Change the NO to YES.
Now, if you were to double-click inside the viewport and zoom, you are still zooming the paperspace, not the model space. This prevents a user from messing-up the scale.