You apply for clerkships and are usually given what you ask for or close to it. A program can only accomodate so many students at a time. So with some of the more popular programs, they may ask you to consider other months. I would definitely suggest clerking at programs that interest you concerning residency. If you have a good month, they are much more likely to choose you over someone they met strictly for interviews.
I will also add that some program curriculums allow for more clerkships than others and some programs will actually choose the months that you can clerk. Students in those programs run into problems when they only have specific months they can clerk and their desired programs can't accomodate them those months. Again, that is just program dependent. At DMU, your entire last year is spent clerking so it isn't an issue.