Mr. Sun will try to explain each point.
For now, Bluetooth is not that popular as it used to be a few years back. When it started gaining popularity it was like magic to most of us. We were in awe when we got to know that we could send files from one mobile to another mobile and that too for free, because earlier to send a file it would cost 5 Rs each image which was least preferred.
Those times we would send only images or songs. Videos were transferred only if we had so much time to spend with each other, it was seldom sent.
1. What is Bluetooth? It's a wireless connection for short range by which devices can communicate with each other. If settings were not proper once the devices were connected you would get complete control of the other phone from your device. So you had to be very careful not to leave it on, lest you are vulnerable to lose data from your phone if at all any.
2. How it is used? Just tap the Bluetooth button which will in turn search for any other device which has its Bluetooth on and will try to connect to that device. After which you can transfer files and even navigate through the file systems of that mobile from your phone.
3. What is the advantage and disadvantage? Advantage- You can receive files, connect to headphones while driving, Bluetooth speakers and listen to songs, you can watch movies by connecting to your TV as well if settings permit. These are few advantages.
Disadvantages- You would be at risk if the Bluetooth is left on (nowadays the phones are smarter, it will get disabled automatically if there is no activity.), file transfer is very slow.
4. Any other useful information. Bluetooth has lost its charm now, it might get revived again in future with some other feature need to wait and see. For now, I use Bluetooth only to connect to my speakers to listen to music.