The main reason why stuff is available in FLAC is so that people can then choose in what way they want to store the music. IF you download stuff in mp3 format, yet you like a lower bitrate, or vbr stuff, it can be done but it is not advisable since you're going from one lossy format to another. Same goes for mp3 to ogg recodes. When you download in FLAC, you get your music in a lossless format, and can choose your own lossy or lossless format in which you like to store your music.
This. End thread.