In a 4x12 one huge thing is, e.g. placing the mic on the top left speaker, but putting that mic more toward it's right side, at the outer part of the cone. Now you're next to the top right speaker too, and you're going to get bleed from that speaker. But what about a 1x12? Then you're talking about the construction of the cabinet and room acoustics. The cab itself will resonate of course, and it's not going to sound uniform to mic all over it's construction. And the acoustics! How is the sound reflecting off the walls, ceiling, and floor? Is it isolated at all? If so, how much? Since sound is so 3D in reality, mics totally track along with that. What I mean by sound being 3D is that something will sound different at every point in space, and, to a mic, unless you painstakingly create an anechoic chamber, which is very rare and, from my understanding, never really used in music recording, you're dealing with some level of the acoustics of a room positively coloring the sound of the cab. Because yes of course the cab is its own sound generator, but to the mic there's no distinction between the cab and the room. It's always the cab and the room. And even if you had a speaker cabinet that could sound the same all the way around it, the spot in the mic where the mic would have to sit to capture each part of the speaker would impart a different coloring of that capture because of the room! It's tremendously fun to think about, but the main thing is, it gives so many more tonal options than one might first imagine!