I use stereo tracks for stereo microphone pairs only. ORTF, AB, MS, NOS (God forbid, XY) etc., these are designed to be panned hard left and right with no alteration in post. I always record acoustic instruments in stereo, you have to in the classical field, it is called the main pair and it is the starting point for all professional acoustic recording (throwing down the gauntlet on that one I bet).
I do supplement with many other microphones for spots and supports, those are in mono so I can easily pan them in the stereo field without a competing stereo image. For instance, when I record an orchestra, I will use a stereo pair in front of the entire group as the main pickup, but I usually have a couple microphones spaced evenly for the woodwinds and brass. Those are recorded on mono tracks because I might not want them panned 100% either way or may need to adjust levels independently. This is a pain in a stereo track, but a quick, basic task in mono.
It really is as simple as counting to two. If you use one microphone, use a mono track, if you use a matched stereo pair, use a stereo track. Stereo synths, use stereo, a mono sample, use mono. It is a no-brainer.
The only exception would be a couple stereo plugins which may glitch on a mono track, but many of those have a mono version of the plugin. Whatever works in that case.