Most of my music on my DAP is mp3s at 256 and 320. I'm OK with slightly lossy music on the go. Its good enough for the airplane and the hotel room. I am fine with that small sacrifice in sound quality to carry a larger part of my library around with me since I am away from home a lot (sometimes up to a week or two at a time).
That is ok... But we are different... 2500-3000 tracks are enough for me for two weeks... And I prefer Flac quality over mp3... Some exceptional good mastering and recording might sound almost the same in Flac or mp3. But in general there is a difference. (Of course it also depends on what headphone you use....)