Last year I started a thread called 'How thick is too thick and how thin is too thin' or something along those lines. I can't really say I have worked that one out, although I have small EDC knives and my new 5" koyote in 0.1", several in 1/8" thick, a couple in 5/32", a couple in 3/16" and a some choppers in 0.25".
When it comes down to it, thin (especially when matched with full flat) is best for slicing chores and food prep. There is just no getting around that one and when food prep is a major component of your knife use then I'd recommend going thin. Thin will also handle the other wood chores fine in 95% of circumstances but will get you in trouble when doing things like trying to pry out fatwood out of stumps and such and are not very good at chopping (unless you have a machete sized instrument). Personally, because food prep is something I do alot, I often tote a 1/8th or now a 3/32" blade for that kind of work.
I will admit to a general liking for a thicker blade though. There are just times when you want to go bumming in the woods on a walk and dig through stumps or hack at branches. Here is where the thick blades come into play. I really like 5/32" and 3/16" thick knives for this kind of thing. Actually, I find 5/32" a good balance between slicing and robustness when meshed with a 4-5" knife. Knives in the 3/16" thickness are great between 5-7" I think. Knives that are 0.25" in less than 6" are not very useful and I have cleared out mine in that range.
Big knives in the 0.25" range are pretty cool. They are heavy and meant for chopping and they do well at that type of activity. They are fun to play with but IMO pretty limited in scope. I like having the RD-9 or SOD in the truck while car camping to come out in play or will take them on a day hike for stump digging/trail maintenance, but I wouldn't bring one of these tanks as a base camp knife if I had to hike in.
On thing is for sure, on the thicker knives, there is a benefit to convexing the edge to improve slicing performance. This is particularly true for the EDC/mid sized knives in the 4-6" range. Convexing a 5/64" or 3/16" blade gives it a massive boost over slicing performance compared to a V-grind.
So I'll sit on the fence of Pitdog's post and say thickness depends on activity. If I see myself doing lots of food prep then I'll go thin for my camp sized knife. If I see myself working on activities that I really expect heavy knife use, like building a shelter or searching out fatwood, then I'd be more inclined towards carrying something in the 5/32" to 3/16" range. In fact, I'm most inclined to have both thickness on me.
[Edit] One of the curiosities is that it is often recommended to have a small thin knife and a longer thicker knife. In the case of food prep, you usually want a longer thin knife so I don't find the above recommendation works all that great. Also, a smaller (4-5") thick knife will suffer far more prying abuse than a long knife of the same thickness. The only thing a long thick knife is really good for is chopping.
