I imagine it would take a lot of discipline to create a bunch of external/reference files by themselves when working on a big scene.
If one has already constructed a big scene, say a kitchen, and you decide that it would be better to reference all the objects in it, how does one best: A) create the external, stand-alone file, and B) set the old toaster to the new toaster FILE ?
I’ve started practicing this workflow myself just recently.
Of course, I messed everything up the moment I changed the path to the hard-drive with all the assets (see here).
That said, one thing I’ve found quite handy is to reference collections.
So, I create a blend file and I have only one collection which I rename, for instance, table. I only leave the table object in it with the right UV maps, textures, and so on.
In the main scene I then only have to link the collection to get all I need.
One thing I started doing for each asset is to parent it to a Null. The null sits at 0,0,0 so every time I link the asset I know its origin will be where I expect it to be and it’s easier to re-position in my main scene.
That’s all I got so far. Hopefully, someone with more experience will chime in.
I’m pretty sure I’m not familiar with good practices of Collections.
In the above snippet, if you could clarify: you have a *.blend file containing multiple Scenes, and these scenes are referenced by the “Main” scene. Is it necessary for the sub-scenes to have the item(s) referenced in Collections per se, or can they just be …oh, I guess there’s ALWAYS at least one Collection, the default one.
Re the 2nd part of my question: if one has already modeled an asset, what’s the best way to get it into its own Scene/Collection, that is, remove it from the original Scene while simultaneously creating a link to it?
Tnx.
I hope I haven’t created more confusion.
When I mentioned the collections what I meant it’s just a way I kind of prefer as opposed to linking directly to a mesh, but that’s just me.
In other words, you don’t need to link a collection. You can simply link an object.
So, in your example, you have linked in your main scene the object toaster from another blend file. If you want to update the object you switch to blender file in the outliner
and then you should see an icon represented by a chain 
Then you can right-click on it and update the linked object, assuming you tweaked the object in its original blend scene.
Alternatively, you can activate the Edit Linked Library add-on. Bear in mind, you’ll be able to see the add-on only if you turn on the testing add-on category.
With this add-on, you can edit directly the object by clicking on the Edit Library button in the sidebar panel (in the Item tab).
Now, all this assuming you are updating the original object.
If you want to replace it with something completely different, I think you need to right-click over the linked object in the Blender File list and choose relocate. As far as I know, this works as long as the two objects have the same name.
I haven’t gotten that far in terms of linking, so I’m not sure if there’s a better way to do this or even a more correct way to do it.