Microphone technique for singers - just say no
Microphone technique for recording engineers consists of selecting the right mic for the job, then setting it up appropriately.
But there is such a thing as microphone technique for singers too. And it has no place in recording.
To appreciate the typical scenario where a singer might use 'microphone technique', imagine a cabaret environment. Las Vegas or cheap cruise - take your pick.
Most singers have difficulty controlling the level of their voice. Low notes come out quiet; high notes come out loud. So the singer will tend to come close to the mic to emphasis the low notes, and back away for the high notes. They judge the level from what they hear on their monitors (or what comes back from the room in systems that lack monitoring, as many systems used in cabaret do).
There is nothing bad about this - it gets the job done. It is possible to use a compressor for live vocals, but the problem is that it makes feedback more likely. So a compressor should only be used where there is a sound engineer behind the console all the time, which for cabaret is often not the case.
If a singer uses 'microphone technique' in the recording studio however, there is a problem. The closer the singer gets to a cardioid mic (most common for vocals), or indeed any directional mic, the more the low frequencies are emphasized. This is just the way mics are.
So if the singer gets close for the quiet notes and backs off for the loud parts, the amount of bass in the signal will vary. This is most definitely a bad thing.
The fact is that a decent mic can take any level the singer throws at it, no matter how close (even opera singers, with a mic that is designed for high levels). So there is no need to back off. The singer should maintain a constant difference and leave the engineer to handle the varying level during the mix with the fader and possibly a compressor.
The only reason to vary the distance is if there is a section of the song that demands a close-up, breathy quality. In this case it is acceptable to come in close. But even here it would be better to record this in a different take as a separate track so that this special vocal timbre can be processed appropriately.