There are purists who insist on lossless WAV (CD) or FLAC and nothing less. But can they really hear the difference from compact formats? Then there is the standard compressed and lossy MP3 128 kbps, which many find just fine. And it produces files a small fraction of the size. And of course there exist many formats in between. Much depends on the quality of the recording to start with, what equipment you have, and of course how good your ears are. And especially, how demanding you are for perfection. But could the differences you think you hear be in your mind rather than in your ears? Personally, I like old music for which MP3 128 kbps is good enough. For newer HQ recordings, I go for 192 kbps. Anything above, I don’t consider worth it.