Well, like any scripting language, Perl is primarily used to "glue" or modify other programs typically written in C or C++. However, unlike something like shell scripting, Perl does actually have functionality beyond that, and is used as a standalone solution by many people. This is the reason I prefer using Perl to other scripting languages. I feel less constrained, and have more versatility in regards to how to approach a problem.
People in the industry nowadays say that Python will eventually phase out Perl, but I don't see that happening any time soon. Not to mention, as long as older systems need to be maintained, Perl will still have a long lifespan. It is definitely worth learning in my opinion, even just from an academic standpoint. I find that Perl requires a different problem-solving thought process than something like Java or C, and can help you develop as a programmer.
I also want to add that when choosing a language, it is better to figure out what you are trying to solve or accomplish first, and then figure out which language would provide the best solution.