This is a very general statement and will not apply to everything.
For the most part, I feel copying and pasting is ok on anything but vocals or guitar lead lines. Those are the two things that really stand out if they're identical. As long as those two things are different each time through that part of the song, the song will sound fresh all the way through for the AVERAGE listener.
Now for instance if I have a song with a really funky bass line that's just all over the place and really makes the song, then obviously I wouldn't copy the bass line the second time through the chorus. You get where I'm going with this.