When creating Groups of elements, Revit creates a default origin point at the ‘center of mass’ of the selection set. It’s easy to simply accept it, name your group and proceed with placing it numerous times throughout your project.
The challenge with the ‘center of mass’ origin/insertion point is that it is so arbitrary: it’s fine when you’re making simple edits to the group later, not so fine when you need to select multiple instances of groups and change them out for alternates. Since the alternates likely ALSO have an arbitrary origin/insertion, based on its ‘center of mass’, they rarely coincide. I’ll go so far as to say they NEVER coincide, so you’ll have to spend time repositioning them.
Set the Group Origin:
When creating the group, look for where the X/Y origin marker appears, and simply press/drag it to your desired location (in plan). As noted in a previous Group tip, it’s good to have a 3D view open to confirm the elements being combined into the group, and you can switch back and forth between plan/3D views to select/deselect if necessary, but make the origin setting in the plan view, so that it associates to the plan level (moving the marker in 3D runs the risk of it snapping to an element edge that is NOT in plane with the level, and things can get out of plane that way)
NOTE: In previous versions of Revit, you had only one opportunity to set the origin of a group. In the current version, you can reset the group origin after it has been created, so don’t leave groups with arbitrary origins!
Good origin selection tips:
Unit layouts – set origins to intersecting wall faces or grid lines at a demising wall / corridor wall. I’ve swapped a LOT of unit layouts, and this has proven to be the most stable reference for full unit layouts, as most variations happen at the perimeter wall.
TR/Bathroom layouts – the corner beside the toilet is the starting point for the majority of key placement/clearance dimensions.
Kitchen layouts – the wall join at an L layout, or a wall/cabinet corner for a galley/center floating layout.
Closets/storage – demising wall connection point, where it would most likely respond to adjacent walls already in place.
The more consistent teams are with setting logical group origins, the more opportunity there is to create ‘swappable’ group options, and reuse groups in subsequent project files.