With any instrument or sound source, the biggest single recording decision to be made is whether is to record in the nearfield or the farfield. These are not just arbitrary words for subjective distances from the source.
The "nearfield" is the radius within which the sound of the instrument is markedly different depending on the location and angle of the mic or listener. The "farfield" is everything outside that radius. The nearfield of most instruments usually ends at a distance about the size of the main body of the instrument itself. So an acoustic guitar's nearfield extends maybe about 3 feet away from the body of the guitar. A drum kit's nearfield extends maybe five or six feet away, and a grand piano's is even bigger.
This distinction is obvious to visualize with a drum kit. If you put a mic right next to the floor tom, it's obviously going to record a lot more floor tom than hi-hat. It is also going to record the other kit pieces disproportionately, according to their distance from the mic. This is "nearfield" or "close" miking. Anywhere we put the mic inside this "nearfield" is going to make a very big difference in the recorded sound, nut just in subtle ways, but in very specific and acute alterations.
In order to get to the "farfield," we have to move the mic far enough away from the kit so that all the drums are heard more or less proportionately, no matter where we angle or place the mic. The mic has to be *at least* as far away from the closest kit piece as the closest kit piece is from the furthest kit piece (e.g. if the outside edge of the floor tom is 4 feet from the outside edge of the crash cymbal, then we should be at least 4 feet away from either one). Changing the mic position or angle in the farfield can still affect the sound, but small changes will not have the same drastic impact on the overall balance as they do in the nearfield. We have crossed the critical line where the individual kit pieces begin to sound like a unified whole.
The drummer's head and ears are in the nearfield, and as it happens, putting all the drums in easy reach has the effect of creating a pretty good balance of sound, so that they are also all about equi-distant from the drummer's head. Nevertheless, the sound that the audience in the front row hears is apt to be quite different from what the drummer himself hears.
This distinction becomes a little harder to wrap your head around (but no less important) when we get into single-body instruments like acoustic guitar. The guitar is shaped the way it is to produce certain resonances from different parts of the body and soundboard. Here's a resonant image overlay showing the vibrations of a violin soundboard at a particular frequency:
As you can see, different physical parts of the instrument are producing different parts of the sound, the same way that individual kit pieces in a drum produce different parts of the overall kit sound. If there were a way to "watch" this happening, you'd see different parts of the instrument's body "lighting up" and moving across the body as different oscillations as various notes and chords sounded and decayed.
So if we point a close mic at one part of a guitar body, we will be picking up a disproportionate amount of the particular resonance of that square inch of the body. Not until we get a few feet away do we get a full, unified, consistent image of the entirety of the guitar sound.
This can work for us or against us. Moving the mic around inside the instrument's nearfield can allow us to highlight certain aspects of the sound, or downplay unflattering aspects of a cheap instrument.