Bitlocker encrypts the drive it is on. It is mostly used in the enterprise because companies don't want employees/ potential thiefs to just steal the HDD and then have all of the data. If you have a password on your PC and you don't have government secrets on the HDD then I wouldn't bother with it. One of the most potentially problematic things is if you forget the pin or lost the string to decrypt the drive then it is essentially useless.