I think it comes down to how fancy you want to get and how spooky the fish are. As JC says, floating leader helps casting a bit, and as you noted, the sinking leader/tippet will tend to pull the fly under during drag/retrieve.

On calm water, I can see a floating tippet, so I figure the fish can too. It and/or its dimple in the surface can cause a shadow. Probably only matters to the spookiest/most-experienced fish.

But I have only invested in fluorocarbon tippet so far, so just tie a piece of that on the end of a floating leader. Just cut back the leader and make more of it fluorocarbon for those popular trout streams.