Well, if I was trying to use my degree (BA with an emphasis in composition), the answer would be 'teaching music' and that's about it (composition isn't a job, it's an illness). I don't do that - the only thing the degree has formally gotten me for employment is the ability to say I have the degree - but informally I have no regrets about spending four years learning about a topic that interests me and that I enjoy.
Music theory isn't hard, but like most systematic approaches to a subject, it does require a base set of knowledge/terminology to start from, and acquiring that base without the benefit of something like piano lessons is kind of hard. I think that's what threw most of the folks I went to school with that had trouble with the topic. Some folks were vocal or wind majors that weren't accustomed to thinking of more than their individual line, and dealing with multiple notes at once was a new experience. Others had learned to do a lot of things by ear, and so trying to give names to some of the things they already 'knew' was the big stumbling block. Finally, a lot of theory ties back into Baroque/Classical harmony, and starts to break down as you move through the Romantic era and into the 20th Century (both for high art music and popular music), so there is a certain amount of 'when are we going to use this' for some folks.