Well I agree with what everyone has said above, so this is a bit of a boring entry.
My take is obviously dioramas, as to me they are 3D paintings.
I also appreciate single model displays on a plane base and do plan to do a few in the future.
The difference for me is all about how i want to display the subject to be enjoyed by me or others (me first). Usually I like to keep it simple as a scene so it works as a display and a 'short story', the approach from the start is weighted by the balance of the composition to make the most of the visual harmony with the color and detail.
If I want to go bigger and consider going 'full Letterman'
, it would be for visual impact around a story with the details leading you around the scene. The overall balance would be the visual hook that would draw the viewer closer because it has that thing that you can't quite put your finger on but you know its there throughout.
Lastly, I would create a model to put on a plain base(no ground work etc,) when I want to appreciate the model purely as a part of a set or a rare collectible, so that all distractions are removed. It would still be visually attractive through weathering etc but would match with others that were displayed the same.
I would probaly only do this for certain types of ship models, spaceships, flying plane displays or single figures. I would never do this for a 1/35 scale land vehicle but would for a 1/16 tank display.
My final word is on those who rivet count or as mentioned by others, dwell on what they percieve to be inaccurate paint or details. I research for the interest and fun of it and it is by no means a religion for me. I have found that most
over-the-top rivet counters are not painters (in most cases but not all) and rivet count for exactly that reason....they lack imagination, creativity and most of all the ability to improvise and interperet real or percieved effects and so turn back to all they know - the engineering side of models.
These types often suffer from being extremely boring while mixed with 2 1/2 cups of arrogance. :fencing
Ian.