I love recording with 2 mics on 1 source. What the heck, we have 2 ears, why not use 2 mics. On acoustic guitars you can mic the bridge and neck positions with matched or different mics and get some amazing tone. Of course, you need to check for any comb filtering effect if that matters for your project. You can also move the mics back about 18 inches or so. I like to set the mics one above the other pointed at the bridge and the other at the neck position. That reduces the "hype" caused by mics closer to the source at a greater distance from each other. The tone remains more "true to the source"

On amps with a single speaker, same deal with the hyped sound or more natural. Inches matter in recording stereo on guitar amps so set your mics and move the amp and you'll hear the difference. It seems that most of the recordings we hear are a close mic so that tends to be the sound we like for our guitars but tone comes alive with 2 mics. If you have more than 1 speaker you can mic 2 speakers or mic the back and front of the amp. Sometimes these mic placements create just the sound you want.

I have a MS Stereo mic that I have used many times on vocals but 2 mics also work. It's is hard to explain what you hear but it seems by adding the second mic you can hear the placement of the vocal in the mix. When recording, the vocalist hears the stereo mic effect and sings to it. You might say it gives the vocal movement in the music. It may not be useful for every song but if you want a natural but in your head sound, try it.

When mixing stereo tracks if you pan them left-right equal, the sound is centered. If you want to move the image left or right just adjust the level.

It is really simple, a little extra care is needed but it is a real education for the ears...you might call it EAR U....sorry