Have you ever renamed a family and then wanted to load it back into a project without having to swap out your families of a different name and risk losing tags and dimensions?
Well its possible.
In your project browser (where all your sheets/views are list at the left of screen) scroll down to the families section and expand the list.
Now find the family you want to overwrite.
Right click and select reload.
Now navigate to the family you want to overwrite it with. Amazingly it doesn't need to be the same name or even the same family category
Once reloaded revit will swap out all your families of this type in the project for this new version.
This is good for keeping file sizes down and avoiding excess loaded families.
Hope this helps :)
Comments are welcome as always.