Check it out:

Pretty interesting, isn't it? I'm not sure if he does this often, but I saw it the other day on a Braves telecast and figured it would be worth sharing. The main detriment of this approach is that it can move the level of your eyes, giving the ball more movement than it really has, making it difficult to pick out the final location of the pitch. It should help with hip rotation and add a bit of power, though.

If Blanco employed the "running swing" technique of Ichiro, it would help him get down to first base quicker, much like fastpitch softball players who use left-handed slap hitting to take advantage of a small infield to reduce their contact-to-first times. However, in baseball, this ability isn't all that important given the size of the infield and the arm strength of most infielders. Employing such a linear swing will also kill your potential to hit for power, but I suppose that's the tradeoff you make.

EDIT: I initially titled this post "Henry Blanco..." which is obviously quite wrong. I was watching a clip of him throwing a runner out at third base (catching mechanics have recently been very interesting to me) and got the two confused. Thanks to rwperu for pointing it out.