I might do that next time I think the chain is past its best. I end for ended it last summer, but the idea of getting a greater length if needed by just adding new is quite a good one, as I only have about 40 metres, (about 140 ft) of chain, although have never needed to put it all out where we cruise.
However, I have thought of another good reason to do it. I noticed when I did the swap around, several of the (otherwise new and never-seen-the-light-of-day links were too rusty to trust, so chopped that last couple of metres off. That was because that was the part of the chain which had been sitting in the puddle of salty water a lot obviously. So if one has one's new chain sitting atop this, then that should not happen, as it would drain and dry better. Of course if able to give it a fresh water flush after a trip out as well - all the better.