Reply To: Understanding the scene collections and heirarcy

[Dwayne Savage]

There are a couple of things you can do.
1. Use multiple collection to organize your pieces. You can also select an object and press shift+g->collection->Then the collection name if the object is a member of multiple  collection. This will select everything in that collection. 
2. Use the [ and ] keys in 3D Viewport. If you have an object selected and press [ it will select the parent of the selected object if it has one. ] will select all children of the selected object. if you want to keep the original object selected then use shift+ [ or ]. Side note: you can use Shift+G-> Parent, Children, or Siblings if you want to select objects that have parent/child relation. To keep the original selected after you click, you will have to either expand adjustment box in bottom left corner of the 3D viewport or press F9 to bring it to the cursor and check extend.
3. Collection/Hidden collection instancing. First, basic collection. move all objects into a collection. click the check box next to the collection name this removes it from the view layers. So, it won’t render this one and everything in won’t be seen in the 3D viewport. Then with mouse cursor in the 3D viewport press shift+a->Collection Instance->then click the name of the collection you removed from view layers. This instance will move and act as one object. You can always active the collection and adjust the objects in it.(Move, rotate, scale, edit, sculpt, etc) Second, the more advance hidden collection. Instead of unchecking the view layer box you right click on the collection and click unlink. You can still add it with shift+a->collection instance->{Collection name}, but the collection no longer shows in the outliner. If you want to access the collection again you have to change the outliner mode(second icon on the header) to blend file. then scroll down to collections and expand it. Then right click on the collection name and click Link to Scene. Then you can change the mode back to View Layer and it is back.