This trip to Germany was the first time I used the TripMode app for Mac. It works exactly as advertised, saving me on bandwidth when I have precious little of it available. If you haven't heard of TripMode, I wrote about it recently, but in short, it's an app that disables internet access except for apps specified by you.
Why is this important? Because if you are stuck in a place with limited bandwidth like I was (AT STUPID NH HOTELS IN MUNICH!!!), sometimes those little bits of internet are best not used for updating files on Dropbox, Google Drive, OS X updates, and other app update checks. If all you want to do is check email through the browser, TripMode makes sure that only your browser can access the internet.
Of course, TripMode also works if your computer is tethered to a mobile hotspot. For $7.99, this app can prevent over-usage of international hotspot tethering. In other words, it can save you money while still allowing you to do what you need to get done.