You'll hear a variety of answers to this question. When I was thinking about doing an away rotation, some would say it's required and some say it only puts you at risk. At Pittsburgh, we were recommended not to do an away rotation, and in part this might be due to the strength of the department and the relative ease of getting letters from prominent faculty. On the other hand, 4/5 of the current intern class did a rotation at Pitt (1 student from Pitt Med). From what I could tell, all of the current interns at Penn had rotated there, and 3/4 of the upcoming class at hopkins rotated there. Known commodities are very valuable for a program. They ensure that the student will work hard and get along well with the residents, therefore minimizing the risk to the program. On the other hand, while doing an away, it's easy to make a mistake, conflict with a resident, etc. If you do well and your application is within the range of their typical successful applicant, an away can be a great advantage.
I think the greatest value of an away is to see how other programs run. I didn't do an away and wish I had, but only to see the difference between a 5 resident/year and maybe a 3 resident/year program. If your home program isn't particularly strong or if you don't have a home program, most would recommend an away. It will be a personal decision. I have heard of more folks doing an away at their top school and not matching there than the other way around; however, my experience indicates that top schools do like students they know will work hard.
