I have some friends who employ multiple choice tests in their philosophy classes. The primary motivation seems to be that such exams are much easier to grade, and I must admit that sometimes, when I'm about to dive into a pool of poorly organized, poorly thought out, illegible bluebooks, I am tempted to follow suit. For multiple choicers, exam day is no big deal; for bluebooksters, it is very very bad. With four classes, I lose an entire week. One friend got on the multiple choice track by giving exams where half was multiple choice and half was short answer/essay questions, and then noticed that scores were highly correlated with one another. So she cut out the essays. She says, "so why am I busting my balls to grade these fucking essays?" She was getting the same information from the multiple choice questions.
I dabbled in multiple choice once back in grad school, and it seems to me that the drawbacks of multiple choice are decisive. For one thing, they require a heavy upfront investment. It is much more difficult and time-consuming to write a multiple choice exam than it is to write an essay exam. You need at least four possible answers per question, where exactly one is definitely the right answer, and the other three are definitely not right, but they have to be close. I find I don't have the knack for this. I found that I ended up mostly writing questions where there was a trick or which were otherwise unfair.
And the other thing is, and this is more important, I worry that multiple choice tests emphasize the wrong things. While I think it is important for someone with training in philosophy to know, for example, what Descartes did and did not say, and to be capable of picking the thing he didn't say out of a lineup, it's just as important for that person to understand why Descartes said that stuff. And I think this is where philosophical training becomes useful to non-philosophers. Being able to understand what the arguments are, how they work, how their authors defend them, and what their critics think is wrong with them is a fundamental part of a philosophical education. And gaining a sufficiently deep understanding of how arguments and patterns of reasoning work that it is possible to apply the lessons to non-philosophical situations is an important benefit of success in philosophy classes. And it is more difficult to demonstrate this understanding in a multiple choice test, and students who are preparing for a multiple choice test are less likely to thereby develop these skills. I'm not saying it can't be done; I'm saying it has to be a very well-written exam, and it would be very difficult and time-consuming to write such an exam. And I've never seen a multiple choice exam that I thought would be effective at this.