This cable is a little unusual, rather than having a USB A plug on one end, it has two Micro B USB connections! What is this for? It's for when you have a "USB On-The-Go (OTG)" device, and you want to plug in another USB device. For example, a Pi Zero or Pi Zero W has a OTG port, as does the Arduino Zero, and anything with an ATSAMD21 that is in USB host mode. Also great for when you want to attach to a tablet or phone with an OTG port.
Sure, we have OTG adapters, but this is simpler, no extra cable required
It's about 25-30cm / 10-12" long, so it's nice and compact.