During my projects with single board computers with embedded Linux like the Raspberry Pi, the Beaglebone Black, pcDuino or the Cubieboard, often happens when I need to use and reuse SD cards to install Operating Systems into the boards. However, if later you want to use that same card as a normal storage unit, you might be surprised when you find out that a few MB or even GB are missing and worst, a simple formatting just won't fix the problem.
This happens because the card was formatted to be used with a Linux partition and Windows simply doesn't know how to deal with that. Fortunately there's a tool for that.