Model groups in Revit can be very helpful in replicating repetitive layout of components such as rooms, furnishings, etc. Groups allow editing of one group to update all of the same definition by adding or removing, even excluding, elements. Groups can be mirrored, rotated and modified with the various tools. Groups can even be converted to Revit links to save a group externally as a stand-alone file, as well as the inverse; attached links can be bound to another file and converted to groups. Nothing new.
Like anything there can be a couple caveats. Groups can impact the project file size if overused and not managed – I like to practice removing group assignment after any editing and duplication is complete. Also, while architecturally, groups generally always suit my purpose, structurally, they can give me issues. I often use many techniques to model a structural frame, such as, Beam Systems, coping framing members, attaching column top/bottom, etc. If I have sloped or angled members, I will generally use reference planes to help with quick placement and rotation of member cross sections. These items don’t generally play well with Group definitions if they need to be rotated, or even just copied. A host of errors can appear that are basically failed constraints for the copy.
While these failings will vary, possibly not even appear, it isn’t a repetitive and predictable use of the tool. Very frustrating. Now, the promise of the tool is efficiency in modeling repeatable layouts; quickly populating models without the repetitive tasks of doing it one-by-one, which is what will be done if it can’t be made to work. However, there is a trick. The copy instance method which uses the Control key in conjunction with the pick button (left mouse button by default), will most usually always work in replicating a defined Model Group, then allowing subsequent modify tools to be used with no error or warning messages. Possibly it may not work in every situation or assembly that can be created, but I am yet to have this trick fail me.
Select the desired elements and create the Group and locate the Group’s origin as needed. Select the Group to be duplicated, hold down the Ctrl key, click-and-drag to copy a new instance of the Model Group. The Group can then be modified by rotating, aligning, etc., as needed. Be sure to set the Group’s work plane and Offset as necessary to assign its reference level correctly. Any edits to the Model Group will be replicated through all copies as desired.