Not so much lossy and lossless, but I am downright paranoid about having backups. I've lost some irreplaceable material in computer crashes. I also like having a 1:1 electronic copy of my CDs, but I have many tracks that are on multiple CDs (up to 6!) and I only need one in easy reach. Among other things.
A custom tag isn't a bad idea, but I'm looking for something dynamic. It could change in either direction. I suspect unless we get a dynamic duplicate tracker, there's no way to do this without some manual input.