Clint,
"Splining" a rod involves finding the strong and weak sides of the blank, length wise along the shaft. All you have to do is hold the rod at a 45 degree angle to the ground while gently holding the tip and applying upward pressure to the middle of the rod. You'll see how the rod blank has a natural tendency to rotate to one side or the other, finally settling on one dominant side. If the rod is built correctly, it will rotate to a position putting the guides either straight up(baitcasting) or straight down(spinning). If the rod hasn't been splined properly, the guides will point out to the sides.
When a rod isn't built "on the spline" it causes the blank to twist as more pressure is put on it. (like during a hard hookset while flippin') The twisting can be severe enough to cause small fractures in the graphite or fiberglass eventually breaking the rod.

I can't see spending $300 on a rod where it hasn't been done properly. It's just retarded. Or it's just a way to sell more rods...hmmmm.