Repetition allows to focus on details, to observe music more as a sculpture rather then a process. Repetition is a very complex phenomea, a sample loop offers a different quality of repetition then a piano phrase, played by a real player. Repetition is a huge world and creating something which is repetitive and still exiting is a challenge. Repetition forces the composer to focus on the essence, since it exposes every detail again and again.

Repetiton is often percieved as boring, which is obvously true for a lot of works. Repetion can be achived extremly easy with computers. Therefore we are confronted with a lot of uninspired non-variations of this theme.

A one bar loop repeating for five minutes must be treated with the same care as a five minute piece with no repetition.

Depends on the target audience. Obviously, dance is a genre where repetition is not only okay, but essential for the dancer. A good dance track needs to have repetitive elements. For a highly focused concert audience, music needs to provide much more sonic detail and change. In my own work, I try to combine repetitive elements on the surface with slight variations and non-repetitive parts in the background, to achive a musical quality wich works in both contexts. Repetition does also quite well if put in contrast with non-repetitive moments. The break is the essential counterpart of the beat in a lot of genres.

To distinguish good and bad repetitive art, one must listen or watch carefully. Repetitive art can be very subtil but the seemingly simple nature of it gives the unexperienced observer the illusion that the art is simple in itself. Unfortunately the mass of uninspired repetitve dance music does not help the reputation of this genre. I would assume, everyone who could see and hear Steve Reichs Music for 18 Musicians performed live would have to agree that this is truly amazing music.

Repetition is building up tension if it does not include variation. At some point this can get very annoying. It depends on the nature of the repetition. A ticking clock is something, the brain can easily ignore, after a while it perceives the constant repetition as a static element, not as motion anymore. With a vocal loop this would be much more difficult to achive.

A perfect loop for me is something I experience as quite static and monumental. I like repetition if it has some kind of meditative character, like a ritual, well calculated and done with thought. Repetition needs an inner balance of power. Here we have that element of dance again, the movement needs to be closed for the next round.

Repetition became easy. Especially perfect repetition. But in classical minimal music there is always an underlying movement beyond the obvious cycles. Each player superimposes his/her own groove, creates longer movements over time, sets varying accents etc. The absence of this hidden layer makes pure repetition created from a sequencer quite boring and this also leads to the notion of anonymity or coldness. But obviously it is possible to create all the necessary subtility also with computers. The composer has to be aware of that subcontext and explicitly introduce it into his composition. I would not say that computers made it more easy, they just shifted the neccessary skills

Time. Repetition only works if you put yourself into a state where you open yourself for slight derivations. Be it the derivation of your own perception or real changes in the music.