Formatting the GoPro's SD card frees up space. But it also gets the card ready for use and keeps the filesystem healthy and minimizes the risk of errors. Here are the various ways to do it on different GoPro models.
The GoPro HERO3+ Black and HERO3+ Silver look practically identical. And while there's a lot of overlap in their features, there are also important differences. Here's a detailed breakdown of how they compare.