Clinical rotations in med school affect your residency match in 3 main ways:
1. Probably the most important is your grade on your third year rotations. If you want to do a surgery, no matter where you want to go, it will help to have an Honors in surgery and good comments from residents and attendings (a few schools have P/F clinicals, but most have at least an Honors). No matter what you want to do, honors in Medicine, Surgery, and your specialty of choice are big positives on your application.
2. On factor that is often overlooked is that your experience on a rotation can often affect your choice of specialty. If you have a hellish time on a rotation and don't get along with the residents or staff, this can change your mind about a specialty. This is unfortunate, but it happens all the time.
3. Away rotations in early fourth year at a program where you plan on applying can increase your chance if they really like you. This depends on specialty (I've heard Ortho puts a big emphasis on this). Also, if you already have a great overall application, anything less than stellar work may actually hurt your application.
Hope I answered your questin. Good luck.