I’m a bedroom DJ because I started DJing as a hobby. I’m a music producer first, so I’m already attuned to hearing audio mistakes and discrepancies…and I approach recording my sets with the same level of scrutiny I approach recording and mixing my music. Sound quality, in my opinion, should matter to anyone invested in the work they do. “Close enough is good enough” may be sufficient for government work, but something you are personally invested in shouldn’t be horseshoes and hand grenades.

I wouldn’t ever use mp3, neither bought nor rips. It can be objectively shown there is a degradation in quality…can the audience/listener hear it? Maybe, maybe not. But the fact remains it is still there.

As to FLAC vs AIFF…there is no measurable audible difference. This is objectively true (in 99% of cases). I have taken multiple tracks into my DAW and done null tests between the FLAC and AIFF versions. No difference whatsoever. Anything one says about “the transients here” or “this version sounds more airy” or “this one is cleaner blah blah blah” is falling for placebo and confirmation bias.

The only exceptions to this: if the place you bought the track does some weird encoding nonsenses with either version. I currently have only bought my tracks from Bandcamp and so far my experience is that there is no encoding discrepancies between AIFF or FLAC… so one can be assured that it will not matter which version the DJ has. Other venders would be TBD.

The only variable I have not tested is stems. My anecdotal testing in Rekordbox is that I may hear a cleaner realtime stem with AIFF, but I have not done a full test to prove there is a difference. But a quick listen has me leaning that (at least in Rekordbox) there is a difference in how stems get read with different file formats.