I agree with everyone above.
Yes, repeats are there for a reason and should always be respected (except in the case of exams where you are explicitly directed not to do them. As pointed already by the other posters this is simply due to time constraints).
The repeats are there for (at least) the following reasons:
1.To give the listener another opportunity to listen to the music.
With a painting, you can sit for hours in front of it examining every detail. But music is time bound. It exists only in the fleeting moment. The performer can repeat the same piece passage countless times for his own entertainment, but the listener has only that single opportunity (or at least had, before recordings became available). Hence the necessity and the inescapability of repetition in music, both in the form of repeats, and in the form of repeated patterns. If you decide this is the reason for the repeat, then it should be a genuine repeat, that is you do not play it in any different way. Grieg Lyric pieces and Brahms waltzes (op. 39) are a good case in point. It can be argued that the repeats there are just that: repeats.
2. To give the performer an opportunity to show off his musicianship and improvisatory skills.
Most Baroque and even Classical music can fit in here. The first time the section is played, it is played as written, but in the repeat the performer is expected to add embellishments and even freely improvise. I am sure Mozart, Scarlatti, Bach and so on, all freely improvised in the repeats of their works. Many complain of Mozart sonatas as being dull piano pieces. Yet the possibility exists that the scores for these sonatas just show a skeleton, and is up to the performer to flesh them up (have you ever heard Malcolm Bilson recording of them?). In pieces where improvised ornamentation an improvisation is not expected (most pieces form Beethoven onwards), you are still required to show musicianship by subtle variations of dynamics and agogics in the second repeat.
3. Formal reasons
The music form may require the repeats, and by ignoring them you are literally destroying the form. For instance in a rondo, the subject must be repeated after each episode (A-B-A-C-A-D-A... etc.). If you do not, the rondo form is no more. (In this case the repeats are just repeats: they are not supposed to be varied).
4. To create a certain effect on the listener.
Music is vibration, and vibration affects the human bodymind in fathomless ways. The constant repetition of certain vibrational patterns may be necessary before certain effects can take place. Especially during the Renaissance, the concept and attitude of a piece that would go on an on forever were widely accepted amongst certain musician/listeners. They simply could not get enough of it. This requires a certain frame of mind. A right-brain approach if you wish. Repetition (and most tasks considered boring by the left brain) tend to switch off the left brain and give the reins to the right brain. In strongly left-brain oriented people this switch can take a lot of time to happen. It reminds me of John Cage’s famous saying: "If something is boring after two minutes, try it for four. If still boring, then eight. Then sixteen. Then thirty-two. Eventually one discovers that it is not boring at all."
I would also be interested in what your teacher says.
Best wishes,
Bernhard.