Great post over at MirrorLessons. Long story short, there is a small improvement in image quality, but it’s only noticeable in extreme cases and at high ISOs, and it comes with massive penalties in file size (2x bigger), and performance (number of shots in a burst before the camera slows is cut down in half, and time to write to card roughly doubles).
Honestly, I don’t see a real-world scenario where the new uncompressed files would be worth it. It appears current A7-series cameras simply aren’t equipped with enough processing power to handle fully uncompressed RAW files, which is a bit of a disappointment. This is a wasted opportunity, because had Sony implemented lossless compression, as opposed to no compression at all, performance would probably have been much better.
The good news is, Sony has already shown they’re willing to work on this to get it right, so maybe they’ll add a lossless option in a future firmware update.