I propose that this technique should be referred to as "desheading".

Comp'ing is short for Compositiong

Basically, it's the process of building a single vocal (or instrumental) track from a collection of parts recorded in different takes. Electronic Musician details it far better than I could: http://emusician.com/special_report/art_vocal_comping/

Not to mention the importance of the material itself. I find it's much easier to fatten a distorted electric guitar part this way than a clean acoustic guitar, since the transients are more obvious in the latter case, which means you need to be careful how the parts line up.

> I used to think tracks had to be preserved

I hear ya. I think that mindset is still appropriate for certain styles of music - certainly anything with a "live" feel, like jazz and chamber music. But the studio-as-instrument approach to music has its place too, no question.

I used to think tracks had to be preserved, and takes recorded end-to-end, etc. Now I consider the recording/production process as an equal to songwriting and performing. Go to an open mike to get your ya-yas out playing end-to-end. In the studio, pick up the scissors and cut, baby! These kinds of techniques can truly transform your recordings. And when a listener hears something special, does he really care whether you "cheated"? I think not. Go ask George Martin.

And in general, even with more varied material, I find it takes no more time than, say, vocal comp'ing.

> I’ve messed it up many times, actually I don’t think I’ve ever done it
> and not found the cut noticeable, esp. if you know it’s there.

Ya, I know what you mean. I've also found, though, that the effect is minimal when you cut like this for double-tracking, because details that stand out on one track by itself tend to be masked when you blend in the second track.

I've also found that playing with the end-points of the clips a little can add transparency. Like, on track 1 I'll slide the clip overlap left a few ms, and on track 2 move it right a few ms. That way the edit points no longer line up exactly between tracks, which can further help hide the sound of the edit.