Blade spacing is used mostly for flash appeal but it can do a lot more. Most spinnerbaits will space the blades far enough apart so you have at least 2 distinct areas of flash. That also happens to be the most stable way for the bait to run because as the blades spin they create torque which is why a bait with large blades turns on its side when retrieved too fast. Now, you can use that torque to create different properties on the bait, for example, you have a 3/8oz spinnerbait on .040 wire but you want more vibration. Well you can shorten the blade spacing, when you bring those blades closer together you get more torque on a smaller section of the wire which will cause it to vibrate more. There is a downside to that however, the problem is putting more torque in that smaller space also makes the bait a little more unstable so it takes less speed to make it lean on its side. The advantage is when fish want a smaller profile you can use smaller blades and still get the same vibration as larger blades. It also allows you to make a more durable bait as you can use a slightly heavier wire without losing the vibration, like using .035" wire in place of .031". You can also go the opposite way, for example you have a situation that requires a lot of flash. Well you can use bigger blades but it makes the bait unstable so you have to slow it down, but if you have room you can space the blades out a little more you spread the torque out over a greater distance lessening the effect of it. I make a single purpose spinnerbait for burning, most off the shelf spinnerbaits will lean to the side or even roll over when burned because of blade spacing and big blades. My burner spinnerbait has undersize blades and a wide blade spacing, less torque from smaller blades and the force from that torque is spread out over a greater distance so I'm minimizing the impact the torque will have on my bait. I hope that makes some sense because Allen is correct, it is kind of hard to explain it without seeing it.