• Live music is often slightly out of tune. If the piano at a small club where you are playing a one night gig is slightly low your band is probably going to tune to that piano. I've read of vocalists with perfect pitch saying that this drove them nuts.
• Perfect pitch often drifts as you age. I've read of people who had to stop listening to music when they got into their 50s or 60s because their perfect pitch was now off and everything sounded wrong to them.
* Analog playback systems often run at slightly incorrect speeds.
* Some instruments are difficult or impossible to tune, so the tuning will vary with temperature. Nobody is going to tune a pipe organ in a drafty church every time the weather changes.
* DJ mixes rely on playing tracks at different speeds to allow for smooth transitions between tracks of different tempo[0], which changes the tuning.
You could do that 20 years ago, but now it sounds way better. You won't notice live anymore, but it's still audible. To be honest, pitching them up with them sounding "higher" is actually better most of the time with House, Trance ... Dubstep/Trap ... keeping the original pitch is generally better.
Yeah I've also heard that it's more of an annoyance than it's worth, in fact I'm not really sure of anyone who has said it's a benefit in any way. It's just not really an aspect of music that people usually enjoy anyway. Naturally, music is engineered more to be relatively pitched rather than absolute
It's useful if you're singing a song that starts a cappella and has instruments join later. Admittedly, this is not common. Only example I can think of is The Smashing Pumpkins - Bullet with Butterfly Wings.
• Live music is often slightly out of tune. If the piano at a small club where you are playing a one night gig is slightly low your band is probably going to tune to that piano. I've read of vocalists with perfect pitch saying that this drove them nuts.
• Perfect pitch often drifts as you age. I've read of people who had to stop listening to music when they got into their 50s or 60s because their perfect pitch was now off and everything sounded wrong to them.