I would suspect that what you are calling "aligning the spine" is in actuallity you are aligning to slight bends in the arrow due to them not being perfectly straight.
The link appeared in my post from earlier its a good read check it out. Good info flowing in. Thanks to all
Whitetail101: For wrapped and spiral bound carbon arrows, your right, there is no real spine to the arrow. With these types of arrow, I don't align to the spine. For all the other arrows that are produced from linear carbon fibers formed on a mandrill there is a noticeable spine. To find this I have an arrow spine checking set up (the classic weight and deflection scale method). Hang your weight with a narrow surface area hanger (small wire) and rotate the arrow to find the spine. Alternately you can use the same method used on carbon fishing rod blanks. Apply force the shaft to flex it against a hard, narrow ridge (counter top edge). Roll the rod slowly down the edge until you find a place where the shaft is harder to flew or skips (slides) rather than rolling.
Most of the woven fiber arrows are pricey and not everyone uses them. For the rest of us with linear fiber arrows, aligning to the spine helps.
Ruttin: I've never heard of a floating method, sounds interesting though. I'm going to have to give that a try.
This may seem a bit strange, however I have found perfect arrows cost me more very fast. I have destroyed so many from shooting groups. I tried a target with 9 small spots to shoot at, but I love shooting groups of three or four arrows. The more spendy the arrow, the closer the group as they say, but then again, I cant afford to buy $120 a dozzen arrows every weekend.
For target shooting to limit my arrow destruction rates, I have been shooting the off brand that sportsmans labels as their own, even though they changed them about 19 months back, they still seem to work. At 50 yrds I can keep them on a pop can. If thats tight enough to hunt by its tight enough of a group for me.