Repeats in music are indicated in scores by a double vertical line and two dots:
Into one that might run to almost seven minutes:
And notice that we are not necessarily seeing much difference in tempo. The first pianist takes no repeats, while the second repeats both halves. It makes for quite a different piece as there is something fundamentally different about a three minute piece versus a nearly seven minute piece.
Nearly every one of the over five hundred keyboard sonatas by Scarlatti indicates that both halves are to be repeated. Just from a cursory glance at YouTube performances of K. 213, it looks as if 80% or more of the performances repeat the first, but not the second, half, for a duration of around five minutes.
We are often told that, when performing minuets with trios that when the minuet returns after the trio that it is to be played "without repeats". But I notice that orchestras often do all the repeats both times in Haydn symphonies, so maybe this "rule" is just one of those many lazy bits of folk "wisdom" that we pick up from our childhood music teachers without ever thinking about.
Repeats are very common in a great deal of music, as I said. Dance music is full of them because sometimes dancers need a lot of music and the easiest thing to do is just keep repeating. So dance music, even when found in a symphony, also has a lot of repeats. But not just dance music. The first movement of nearly all Classical symphonies has a repeated exposition and sometimes both parts are repeated, especially in the earlier symphonies. The same is true of piano sonatas, string quartets, trios and any other music using first movement sonata allegro form.
The polar opposite of this kind of music is the continuously developing kinds of music that we find in the later 19th century and for a lot of the 20th century. You could probably create a graph of the quantity of repetition in music that would build steadily through the 16th through 18th centuries, reaching a peak in the late 18th and early 19th century, and then dropping sharply with the later Romantic composers like Wagner and Mahler. It would reach a nadir with some of the music of Schoenberg and Webern where there is no exact repetition whatsoever. These composers attempted to balance the lack of repetition by devising intricate structures in which there is a kind of continuum of similarity by the use of fixed interval sets.
But this did not last a terribly long time and when repetition returned, it did so with a vengeance. The whole idea of "minimal" music is to have a lot, A LOT, of repetition. Here is an example from Steve Reich:
Another composer who is famous for his repetitions is Philip Glass. After browsing through the three CD set "The Essential Philip Glass" I had the distinct impression that for two or three decades he pretty much kept repeating the ascending minor third:
Don't believe me? Here's some examples. Ok, the first one is descending not ascending:
Ascending minor thirds:
In this one the minor thirds are mixed up a bit:
Ascending minor thirds:
Ascending minor thirds with a syncopated rhythm:
And now, in a major departure (heh!) minor thirds alternating irregularly with major thirds in the first movement of his Symphony No. 9:
And I haven't even mentioned Electronic Dance Music!
I think that aesthetically, repetition is extremely effective. A lot of repetition with just a bit of variation for spice is one of the most successful strategies in composition. The most common mistake a lot of young composers make is to wander aimlessly from one idea to another with little repetition to tie things together, just blundering on, one theme after another and all of them different, without anything to link them, blathering on and on and on...
Well, you get the idea. But if, on the other hand, you decide to use ascending minor thirds over and over and over in your music, decade after decade, well, you can do pretty well. Apparently...