Bluetooth used to be a bit of a battery killer, but with the introduction of Bluetooth Low Energy (BLE), that all changed. Over at Adafruit, Collin walks you through a few different ways to use Bluetooth in DIY projects.
We all know that Bluetooth is a way for two devices to communicate with each other, but it's not like its the only communication protocol on the block. BLE isn't just about using less power. BLE only connects as needed, so it's great for periodic updates, like reading from a sensor, but it's not good for streaming anything. More importantly though, BLE support is wide-ranging, which means you can easily access it from just about any device.
Of course, this is an Adafruit video, so the video shows off how to use Adafruit's free Bluefruit app for controlling DIY Bluetooth projects. The video walks through a few different DIY projects that you'd want to use Bluetooth Low Energy for, including in a temperature sensor, a remote control for a car, an RGB colour controller, and using BLE as a beacon.
Even if you don't want to use Adafruit's app, the video's still useful in walking your through when you'd use BLE instead of regular Bluetooth or Wi-Fi.
Collin's Lab - Bluetooth Low Energy [YouTube]