Dynamic range compression isn't new, it's been used by recording, mixing, and mastering engineers for many decades. A little bit of compression is fine, but over-compression can sound downright ugly. Most of today's music, whether it's on LP, CD, the radio or iTunes is over-compressed. Most remastered CDs are over-compressed.
Before we go any further, I'm not referring to the lossy compression used in MP3s, or lossless compression used in Apple Lossless. They've got their own set of problems, but dynamic range compression is a very different predicament.
To the casual listener compression can sound "good," mostly because it makes the music seem louder and punchier, and once music's natural soft-loud dynamic shifts are squashed flat music is easier to hear in noisy environments like cars or over iPods. Compression reduces the need to adjust playback volume--because it's always nearly the same volume--loud.
Engineers worry that if they don't compress their recordings the music would seem too soft and low. That is, if a music listener went from really loud, compressed music to quieter, uncompressed music they probably wouldn't like uncompressed music--unless they turned it up! That way they would hear the music's natural soft-loud dynamics.
Unfortunately, that's not an acceptable scenario to most engineers or record labels. They're addicted to over-compression, it's a hard habit to break.
But the unnatural onslaught of compressed sound obliterates musical nuance, delicacy and emotional power. Compression's loud-all-the-time nature sucks the life out of music.
Here's a great video that demonstrates the evils of compression.
Well, it's one thing to describe the ill-effects of over compression in words; this excellent "Loudness War" YouTube video adds a visual perspective to make compression's destructive properties easier to understand. Like most things on YouTube there's a bunch of videos that explore the evils of compression, but "Loudness War" is one of the better ones.