Traveling with an external battery is beneficial for the obvious reason that it gives you more battery life to use while you're on the go. The real value, though, is what that extra battery life can allow you to do. Especially now that the majority of commercial airlines have made Wi-Fi readily available for passengers, time spent traveling can be nearly as productive as time spent in the office working.
There is a range of external batteries available for whatever your lifestyle demands. Whether you need a small portable battery to provide a couple quick charges to your cell phone or you need a powerful lithium-ion battery to add over 10 hours to your laptop run time, external batteries provide a benefit to all.