Think of the difference between the delicate Japanese knives used for slicing through sushi/vegies and the more robust German Chef knives used for hacking through whole chickens. You could also compare a splitting wedge to a wood splitter or axe. Knife design should always follow function. The thicker the knife, the more abuse it can withstand but at the same time, as the blade gets thicker, it loses its ability to cut.
Thicker blades usually use softer steels such as 5160 because they can handle much more abuse without chipping or breaking. Their form follows their function.
Thinner blades usually have much harder steels such as 1095 because they will hold a thin edge better. The thinner the edge, the finer the cut. But they are also made with the understanding that the user will not hack/chop with them.
Here in the Western culture, we have become acclimated to think that a thicker blade will always outperfom a thinner blade, usualy because of the cheap chinese steel that comes in crappy Chinese knives. But as a custom knifemaker, our job is to design an edge that's best suited for the object that it is meant to cut. If I were building a skinning knife, I would want it as thin and hard as possible, knowing that the knife would only ever cut meat and hide, witht the occasional contact with bone. If I were to build a chopping knife, I would want a little bit of "meat" behind the edge to decrease the risk of chipping, but that would also decrease my ability to slice.
Of course, the steel choice also plays a big part in this equation. If you are looking for a steel that can take a super fine edge and still be very tough to reduce the risk of chipping, then I'd go with a steel such as 3v. The reason why we have so many steel choices is that there isn't a single steel that is best suited for every occasion.
When I design a knife, my mind usually follows this type of pattern:
What will this blade be used for?
How thin can I make the edge?
Which steel is best suited for the edge thickness?
Don't get caught up with the hardness numbers. Each steel has an ideal hardnes. If you want a harder blade for fine slicing, pick a steel that can get harder without chipping. If you want a thicker blade that can withstand abuse, pick a steel that can be softer, yet tougher.
