Open application

It can often vary depending on subject and college. My friend had an open application and was only interviewed at one college, where as I specified yet had interviews at two different colleges. College is initially decided through a computer program that allocates open applications to colleges with fewer specified applications in regards to the college size. I have heard that colleges such as Girton, Newnham, and Murray Edwards get more open applicants, the former due to it's distance, and the latter two due to being girls only so this could be something to keep in mind if you want to specifically avoid these aspects. Having an open application wont affect your chances of getting an offer, so it's completely up to your own personal preference, and even if you do specify you could still be pooled to a different college. Hope this helps somewhat!