Able,
I think I understand what you are asking. Why use a larger spinner bait than a smaller one?
A larger spinner bait is a much more practical all year presentation. As Glenn said, he only downsizes after spawn. With the larger spinnerbaits you can throw these things through the thickest trees, "Crashing them through" that a smaller weighted spinnerbait would hang up in. I also find it a little easier to slow roll these baits when you are fishing deeper water and you also will ctach all sizes of bass on a 3/4 oz bait.
When we were fishing the 8-12" fish wouldn't keep off them. It was getting so bad by the end of each day we were yelling at the dinks, or reeling in faster before they hooked themselves. It was pretty comical.
Larger baits will attract the mid sized fish just as well as a 1/4-1/2 oz bait will.