HZPiano I cannot think of explicit advantages or disadvantages, it probably is more about taste and what amount of bounce an individual player can tolerate.
I found it extremely irritating on an Kawai ES8 (or 7 or something like that which I don't recall at the moment).
Upon returning to position, the key will reach the normal "up" status, overshoot that and bounce back as if a little bit pushed down (without sounding a note), go up again, overshoot again (less than before) and repeat the cycle a few times when I was playing forte. I don't know whether or not it had mechanical disadvantages, but to me that was an unplayable instrument for everything but the very simplest stuff and I wondered how anybody could like it, which many people did. At the time, I blamed the possibly worn out demo unit and the fact that it was mounted up high above other instruments, at an angle facing the player rather than purely horizontal as most people would do.
I have never experienced anything so bad on anything, and I have never experienced anything like that even to the minimal amount on acoustic instrumens.
Johnstaf This is often seen on concert grands at the bass end.
The way that I've seen on grands (not concert grands which I never had the pleasure to play) is that it does something similar but never overshooting the final position, and always stopping after exactly one bounce (and often does not bounce at all). Very different feeling on the fingers and sight.