Copy-pasting minor art sliders (e.g. a wave slider)? Sure.
For everything else, it depends. In most cases, the music has to sound almost exactly the same for it to be justified. Most of the time, copy-pasted parts need to be close together on the timeline and in position without modification, or they need to be rotated much or flipped. Not sure if I made that clear, but hey...
Three pastes (and one of the source, making four repeated patterns) is my general limit. One paste is good for a section close on the timeline.
One good use of copy-pasta IMO was in
Date of Rebirth. There were six identical sections in the song, grouped in two's. I mapped three different patterns for the first three, and copy-pasted them into the last three. Each pairing was unique, and the repeated patterns were flipped and adjusted so they flowed better with the other pattern in the pair.
Another perspective of copy-pasta: copy-pasting patterns, but changing spacing and the type of notes. The absolute best example one could ask for is
Unity at 00:35:482 (1,2,3,4,1,2,3,4,1,2,3,1,2,3). foul's use of this pseudo-copy-pasta makes a somewhat confusing timing pattern so intuitive because you learn as you play.
Bleh.
I have no grudge against mappers who use copy-pasta except in the case where either (1) it makes the map sound weird (
ahem) or (2) it just plays poorly. I'm too tired to come up with examples of good and bad "real" copy-pasta at the moment.