A postgraduate degree often offers a much wider range of options than an undergraduate one, though of course, you still want to specialise. Many universities will allow you to take modules outside of your subject/school for credit, so long as you can justify it and there's space. Even if they don't allow it for credit, tutors often are fine with having an extra person sitting in on seminars and lectures purely out of intellectual interest.
But what are the advantages of taking a module outside of your school/subject - and just how far outside it should you go?
Background and Context
Sometimes there's a clear reason to study something outside your usual remit, and that's often to provide background or context to your work. For instance, if studying religion, it may be useful to take a history module on a particular era - like the Renaissance, or an module in art history to better understand idols, and so forth. You might even want to try out a new language
! In cases like these the benefit is clear, it's easy to justify and you'll almost certainly have no issue getting involved in the course. It's well worth looking into things like this, since having a broader knowledge of the background of something you're specialising in can come in handy, and open up paths of interest that you may never otherwise have discovered.
It may well be that your subject relies on a lot of concepts from elsewhere - perhaps if you're doing theoretical chemistry, you may encounter a lot of background physics you'd like to check up on. Again, this is very similiar to the above in that it's easy to justify and can make a huge difference.
Maybe you're just curious - whether about the subject matter or the school of thought it's in. Maybe you're considering swapping over to another area in future, or you simply want to do something beyond your usual scope. This is a tricky one - most universities will be okay with this, but perhaps not allow it for credit. A big factor in this is how good your work is. If you're already struggling, this is a hard reason to justify, but if you're flying through there's a good case for letting you expand your horizons. Remember: even if you can't take it for credit, you can probably get permission to attend the lectures at least.
If you're considering taking something outside of your subject out of boredom, it's really not the best solution. It'll be a temporary fix at best, and you want to try and find the actual cause
- why are you bored? Is it the subject, the university or just the particular area you're currently working on? If you feel comfortable, try raising it with your tutors - they may well have some options for you, such as setting more challenging reading or helping you swap to a module of more interest. Being bored of your course can be fixed, but not by picking up odd modules here and there.