Why should I use it?
Lossless vs. lossy
Simply put - Lossy codecs achieve great compression ratios discarding your audio data.
So there is no doubt - lossless is the winner for those that want to preserve their audio in original state. Because of that FLAC is very popular for archiving CD audio collections.
FLAC vs General lossless compression
FLAC is audio compression codec and uses specially designed audio algorithms. That makes it far superior in compression over general lossless algorithms like ZIP or RAR.
Extracting from archives such as ZIP has to be done prior to playing and that makes those algorithms extremely unpractical for audio usage.
FLAC vs. Other audio lossless compression
As quality is not an issue in any lossless compression (data suffers no loss), comparison between different lossless audio codecs is usually restricted to compression ratio, speed, market support and possibly some extra options (FLAC for example can be streamed).
Speed
FLAC is the speed king of lossless audio codecs.
It's decoding speed is fastest of all, it uses simple math algorythms that result in great performance on all even old or not so powerful hardware.
Encoding speed is not that important. Because you can only increase encoding speed by decreasing compression levels, our stand is that you should not use fastest encoding speeds in any lossless compressor. FLAC has fast speed modes, but we won't use it. We will use maximum compression levels, take your time, you encode your file once, and as for the future, FLAC won't decompress file any slower no matter what compression level you used. That's the beauty of it.
Market support
FLAC is very well supported codec, and we ask you to join in :)
Being open, free, tested, well performed and well documented makes it ideal for almost all audio usage.
It is available on Windows, Linux, BSD, OS X, BeOS, OS/2, and most of the other operating systems.
It is format used by European Broadcasting Union for the distribution of high quality audio.
It is supported by rising number of hardware devices and is implemented in hundreds of software applications. Increasing amounts of memory brings high fidelity audio and FLAC as it main representative to portable audio devices that are still bastions of low quality MP3 sound today.
Check this list for overview of some hardware and software supporting FLAC
