I'm wondering the same thing. File size just isn't an issue anymore with the cost per gig where it is. What tags can you apply to a FLAC file that you can't to an meda player file?
It isnt necessarily an issue when streaming, as we are discussing, but when loading onto a DAP device with limited storage space it is definitely a benefit.
Applying ID3 tags to wav files has a history of causing errors in the WAV container. Honestly its been years since I have attempted to do so since most of my listening has been through tagged flac files (through WinAmp and Rio Karma). Most players will allow tagging but it isnt part of the WAV metadata as it is with a flac file. As an example, every week when I travel, I simply drag and drop my flac files with tags onto my Karma and I'm off. No decoding and retagging of files is required and I am not creating more files to have to later delete to conserve space.