I double up quite a bit. I usually use 2 # 12 corkies. I usually do it when the water is dirty to get a larger profiled bait. I mainly use 2 contrasting colors also. red/green pink/chartuse and luminous peach/red.
I use a lot of double # 10 corkies for chinook, It gives me a larger profile when using eggs, I dont need to use as much bait that way. It sure helps save on egg use.
I also like using a small corkie under a spin-n-glow. I use the corkie instead of yarn for added contrast and color. Yarn has a tendency to tangle and stop the spinning drift bobber from spinning