I didn't see the benefit of them for many years, then bought some 1.75 4.4s this past year and was very impressed with the stout springs and how balanced the trap fired, and hold I got on yotes with them. I may convert many of my 2-springed coils now over to 4 coils if it will help them perform like these did.
I agree with rdfox though that they probably aren't all that necessary for smaller game animals and smaller trap sizes. I've seen articles on them used for #1 coils on coon even, so possibilities are endless...