I can hear a difference between FLAC and mp3, even if the mp3 is high bitrate.......and I don't use headphones.
Neither of my sound systems cost me literally thousands of dollars, but they are Yamaha and of reasonable quality (if somewhat old now).
I've had 1 particular pair of speakers for many, many years now......Richter Harlequin Mk2's.
They've got aluminium voice coil tweeters and are quite nice for music considering their age.But then they were not mass produced in some massive factory back then......and they were matched as pairs in factory when tested.
I've honestly wasted way more money on PC's and related hardware in my life than I have on audio gear.........at least you can get your money's worth from it if you really enjoy music and decent quality sound (like for movies).
Even if you're talking about pre-HD compressed audio, I can tell the difference between mid bitrate Dolby digital 5.1 and high bitrate DTS 5.1.......and LPCM is different again.
But then if you're only using desktop computer speakers/surround setup (whatever quality) I guess you could get away with the lowest bitrate possible and still think it's sounds the best it possibly could
mp3's are good for portability, but if you want high quality sound and have the means to appreciate the difference, FLAC is worth a little HDD space (which, less face it, is cheap as chips).
The same kind of arguments can be made for compressed video formats.......quality versus small size (and portability).
And if all you have is a screen that can't even display 720p (1280×720) then HD video formats are a waste of time.
But even with all the right hardware and high quality audio/video, if your eyes and ears aren't 100% then maybe it's all pointless anyway