There appears to be no case to have a post that only has the personal-preference tag, since it's completely unclear what that would be about (apart from a personal preference regarding something). It's like the weak version of subjective.
Also, given that Programmers.SE is about subjective stuff anyway, it's also a little redundant. For example, you may as well ask: "What's the best setup for a three monitor workstation to do software development?" It's not like you'd expect anyone to give an objectively verifiable definitive answer.
My proposal then is to remove the personal-preference tag from all posts that have it and ban it if possible.