Especially for opera, where the acoustics of the space have a huge effect on the voice. The Italians use the term "chiaroscuro" to describe it (the term is also used in visual art, but a totally different thing, obviously). In a large space, the audience can hear the vowels very clearly as if the singer is standing close to them, but the distance also gives a darkness to the sound that you just cannot get from up-close mics. It is very difficult to replicate this in a recording.

That's interesting to hear how it changes the way you play as a result. The microphones used also can color he sound differently, depending on what you get. Many of the commercially available mics will have a "bump" on the frequency response around the 2-3kHz range, which will make bad vocals sound very clear. But for an opera singer, who is trained to accentuate that frequency, it gives the voice a harsh edge that isn't really there. When I first discovered this problem, I adjusted my singing to make it softer, but of course, that's now how the voice is designed to be used all the time.

Still, I love the challenge and discovery of how I can achieve a better recording sound. I'm not anti-recording, but I am a bit of anti-perfectionism in the process. This is why I love Vladimir Horowitz: many of his recordings he did in one take and would leave mistakes in there. It was more authentic, and no one thinks he was a hack.