The easiest example I can think of is Blender. When you select an object in Object mode, it draws an orange outline around it.
This effect seems like it would be useful for selecting an object.
How would I do or emulate that effect in Unity?
Make a second model a little bit bigger and set it as a child of the original. Change the material of it and add color. Set collider off. Use a script to make it appear and disappear on mouse over or use triggers or whatever.