Always Be Charging. A mantra that I held to long before I heard it codified in a catchy A-B-C slogan.
For me, it’s about efficiency. If I’m sitting near a power outlet, and I have a cord handy, there’s not much of a reason to not plug in. It’s there, I’m there, let’s top off.
Think about it this way — how often do you hit the critical low battery light on your devices when traveling, and think “Gah, life would be so much easier, if only I had an extra (10 minutes|20 minutes|hour) of battery life!” — well, you can! Just charge, even when you don’t need it.
Sure, it’s a minor inconvenience to be tethered to an outlet instead of milling about with your phone, but even that can be negated with a travel battery. The Anker Astro line has some terrific models to pick up, normally for under $50. With a single Micro-USB cable, I can charge my tablet, my phone, my Karma wifi hotspot, and even HP’s Chromebook 11.
In the end, it’s a hedge. Will it be needed? Not every time, no. But is the minor inconvenience of charging better than a major inconvenience of your battery dying on you? Well, that’s up to you.