As someone who has also posted many long messages that aren't the type of thing everyone here is necessarily looking for, I feel left out of the criticism. I feel that I deserve to be ridiculed at least equally to anyone else, OK? Thank you.
That said: There's certain technical information about microphones and sound that's not too complex, that isn't just a matter of opinion, and that could help people avoid bad decisions. Many microphones are designed for use in specific types of applications--and among different applications, sometimes the design criteria conflict. What makes microphone "x" good for its intended use may make it a lot less good for other uses.
As one example: Many people know from their own experience that ordinary, directional microphones with full low-frequency response for music applications will sound "boomy" if used for close pickup of speech (e.g. in a public address system). But the opposite situation is true, too: Directional microphones designed for close placement will generally sound bass-deficient when used for music pickup at greater distances. Even high-quality microphones from first-rate manufacturers tend to sound thin if they were designed to have neutral/normal response with close placement, but instead you use them for more distant pickup. It has nothing to do with how "good" the microphone is, and everything to do with how it was designed to be used.
Or another example: Microphones that have big peaks and valleys in their off-axis response may have a lot of "character" close up (i.e. when used for solo vocals in a relatively dry studio or voice-over setting) but give unpredictable, sometimes rather bad-sounding, results when used at a distance from the sound source(s) in reverberant spaces. Much / most of the sound energy reaches them arrives at random-ish angles, where their on-axis frequency response--the smooth-looking graph that gets printed--doesn't apply. Unfortunately you have to know how to read a composite polar diagram to see this problem, and the manufacturer has to publish such diagrams (at various frequencies, not just at 1 kHz), and they have to be honest.
Having a prestigious brand name, and a visual design that looks good in a photo with a well-known singer using the mike close-up, won't alter these facts. But from a lot of what I see on this board, it can apparently be hard for certain individuals to accept that not all delicious-looking treats are meant for you and me. A microphone can only pick up some part of the sound field around itself; microphones can't/don't reach out and sample other parts of a space, and they don't respond to our intentions and wishes, but to what their construction does with the sound field around them.
Beyond that, we can talk about stereophonic perception, but not to the point where there are deductively valid statements about What Should Be Done in most situations--only personal advice which may miss the mark because maybe you're looking for an entirely different sensation from what I'm looking for. It's not that "everything is a matter of taste and opinion" (although a lot is); it's also that recording situations differ so much. Someone earlier in this thread made the point that you need more than one recording approach if you're going to deal optimally with the range of situations that you'll encounter, and I really agree with that. Sure, when I've just discovered or rediscovered some approach, I get enthusiastic about it--but the old saying about "to the person who has only a hammer, the whole world can start to look like a nail" still applies.
Finally, just to say something about the actual topic, I use two microphones whenever I think I can get away with it. I usually find that musicians like the results better that way, and being a musician myself, I agree with them--but I'm not entirely objective about my motives; laziness probably deserves some credit along with idealism.
To me there needs to be a very strong reason to mix anything in with the two main mikes. If I'm just not hearing something clearly enough, that's the main justification. And then those mikes need to be close enough to the "missing" sound source that they specifically pick up what they're aimed at, and don't mess up the overall stereo recording. For spot miking I nearly always use microphones specifically designed for close pickup, i.e. directional microphones with reduced low-frequency response. And I never, ever mix live; I record each mike on its own track, then mix at home later, even though that takes a lot of time, because a lot of what you have to listen for is the type of thing you can't hear over headphones, and also because no initial settings are ever perfect, but any corrections that you need to make will be audible as changes in the mix. -- If a person wants to make multiple, parallel/alternative stereo recordings (i.e. not mixing any signals), for sure that's a good reason to use multiple microphones or pairs of microphones, of course, but I don't think that anyone here is questioning that.
--best regards
