These tools simply make identifying and correcting tags easier. For me, it's mostly about ripping CDs I have that aren't in the CDDB (tango imported from Buenos Aires, etc) and these tools make naming them after a bulk rip much easier. But I can also see their use if you have aquired significant amounts of music from the internet and want to standardize the naming conventions of the tracks, sort into folders, etc.
When I run across a disc that isn't in CDDB (happens often, as there aren't a lot of classical listeners among contributors to FreeDB or Gracenote), I add it myself. Takes five minutes.
When I store files on a fileserver, I symlink it in ever relevant way I can think of so that I can access a file structure by performer, composer or major works contained on an album. This also takes about 5 minutes and gives me amazing flexibility for finding any particular piece of music.
Operating systems with filesystems that don't understand symlinks are fucking retarded.
I like FLAC, but if I bog a system down enough, playback goes to hell. I like Ogg, since it supports multichannel audio.
Apple Lossless just pisses me off. It won't play in ANYTHING I use. AACs are almost as bad, simply because an AAC is a container format that might have Apple Lossless in it. APE pisses me off, since most of the time APE files are provided as a large file with a CUE instead of as single tracks, and beyond that you get into weird crap like WavePack, which pisses me off because I have to go looking for a converter or something.
dbPowerAmp can convert anything into a non-sucky format. APEs and m4as and AACs and other stupid formats can be changed to something decent with as little as a context-click.
I don't know how it knew the tag info. But it found the tag info for just about all my albums. The only ones it didn't find were the him albums. It even pulled the album art. My guess is it pulled the info from windows media player.