One of the maxims in karate (good karate that is) is that there is no wasted motion. We do not chamber punches to look good, rather there is some reason for doing so. Something that robs the opponent of their momentum and gives you an advantage. For instance, the chambering motion for a downward block (gedanbarai) can be interpreted as an offbalance and drag-by that places you behind the opponent in position for a choke (ushirojime) or drag-down (ushiroate). In aikido parlance we call this type of motion release#4 or release#2.
One of the really cool things about this interpretation of the gedanbarai chamber is that it makes karate kata a constant reminder of your priorities when attacked - your first thought should not only be to slip out of the way, but also to get behind the attacker. That is one thing that the gedanbarai chamber does for you and it is one reason that it is repeated so very often in the kataset.
I don't know if this particular kuzushi and drag-by is one of the oyo in Rick Clarks intriguing book, 75 Down Blocks. I haven't gotten a chance to read it yet. But this 76th down block is what we worked on today in both karate and aikido.
[Photo courtesy of Marius]