Well, if you're a musicologist it means you've discovered a way to become employed at a university.
It could be a variety of things. I know someone who specializes in Debussy. She has analyzed his work in ways that, I assume, have given her a much better understanding of what makes Debussy's music what it is - and why it is (or was) so unique.
I think a lot of it is simply a matter of trying to figure out what makes music "tick". Identifying commonalities, divergences, confirming hunches, satisfying "nerdy" curiosity. On a more practical level: helping to settle plagiarism lawsuits.

But it can also help with pinpointing changes in a music's evolution. To me this stuff is, indeed, most interesting when it's combined with cultural aspects (such as semiotics). Otherwise, yes, it can be pretty dry and academic.