This feature is intended to allow us to acquire information from another project file and add it to our current project. There are two methods, Views and 2D Elements. Both methods involve selecting a project file first. To get started you choose the File menu and then Insert from File.
The first option, Views, grants us access to views and sheets. The catch is the views are 2D views like drafting, detail and schedule views as well as sheets. The sheets must either be empty or contain only 2D views. In the past I posted an article describing using this to deal with dummy sheets to fill out a complete drawing list. This feature presents us with a dialog listing the eligible views.
It is a great way to transfer office standard detail sheets and schedules into a new project. When you select a sheet that includes just 2D views Revit will bring the sheet and all the views on it into your project as well as placing them on the sheet.
For campus projects that share details it allows you to place copies of the details in each building file so you can create intelligent view references to the details. If you only change them in the "master" file (a primary building model project) you only need to keep the sheet and detail numbers coordinated if you do all printing from the "master" project file.
The second option, 2D Elements is intended let us "steal" drafting annotation, detail lines and detail components from model views. Imagine a wall section that is the same or very similar to the one you are working on now. Using this tool you can grab the 2D embellishment in the other project and added it to your current model's view. This tool presents a dialog of eligible views too, all views that have any 2D information added to them.
Annotation that requires a reference like dimensions or tags will likely fail to insert for fairly obvious reasons, namely the reference isn't necessarily in the same location or even present.