Every year, I mentor a few dozen people who all ask for my thoughts on one question - should I leave? I work for a pretty large company, so some of the advice I give can be applied more generally to anyone working in a big firm deciding between external options and an internal career path. So here's what I say ....
First and foremost, follow your passions. If there is an opportunity that fits with something that excites you and gets you blurring the boundary between working for a living and working for fun, jump on it and everything else will come naturally. If the opportunity doesn't exist, maybe you should create one. Whether you've always wanted to be your own boss or work in high fashion, passions are callings you should obey. If your passion doesn't fit the opportunities available inside your current company and you are unable to create one, it may be time to look outside.
Second, avoid stagnation and vitriol. If you feel you are not growing, feel you can "do better", are dreading coming to work or are feeling bitter about your employer, it may be time to look outside. I counsel folks who complain about their work and their company incessantly to ask themselves why they stay any longer. If you are facing stagnation or vitriol, you should do you and your employer a favor and move on. Now, don't get me wrong, it's always good to find a way to get your concerns heard and instigate change. But you should not make yourself out to be the victim if you can't. I also advise folks to look inside themselves too - sometimes it's the mindset and not the environment that causes these feelings. That's something moving companies won't solve.
Third, step up growth opportunity. Lateral moves don't make much sense to me (unless you are following your passion or looking for a fresh start per above). Usually, I advise people to look for step jumps in their growth - a larger scope with more direct impact, an exciting new category, or even significantly higher pay. Large companies often have a ton of opportunities to continue to grow in a professional career and it takes time to build up credibility and connections within them. It's smart to look inside to leverage that credibility and connection before jumping off. But if the external roles do offer that step jump, go for it.
Last but not least, get a life. Everyone has different personal values and goals - see my post on The Balanced Lifecard. But you should stay true to yours. Time matters - if you value staying connected to your wife and kids, you may not want a role that requires you to travel 3 weeks in a month. Pay matters - if you are looking to fund your kid through college, you may not be able to afford working part time. Location matters - if you need to be close to elderly parents in another location or even a pastime you enjoy, you should move. If your existing employer is unable to meet these needs, it may be time to look elsewhere.
All of the above assumes you have a choice of course. But if you do, you could do worse than start by considering the above four points.