The concept of handle to blade ratio is primarily a "looks" or "art" reason.
I won't argue against that, but I'm happy that you put in the word "primarily" as it leaves some room to take the functional aspects of handle to blade ratio into account.
In my point of view the handle to blade ratio affects function at least in two ways.
1. Folding knives are meant to be carried in an unobtrusive way. To me this in an important part of their function. When carrying a knife in your front pocket size matters. A bulky handle might offer a very ergonomic grip but at the same time will make it impossible to carry the knife in a low key fashion. Therefore I usually prefer handles the size of which matches the size of the blade. If I want to carry a large blade I will have to put up with a large handle obviously, but when carrying a slim and/or short blade I would prefer the handle to be slim/short, too, in order not to attract unwanted attention. Of course this is a personal preference but to me it has become one of the most important aspects when choosing a knife for EDC.
2. A discussion of handle to blade ratio should take the aspect of balance into account. I do like a well balanced knife and so do many others what - at least in part - acounts for skeletonized or tapered tangs or liners. A skeletonized liner helps to reduce the overall weight of the knife but also adds to the balance of the knife by reducing the weight of the handle. This moves the balance point closer to the blade which again makes the tip more maneuverable. Balance allows for precison and this a good thing. OK, we're not talking about swords here for which the question of balance is even more important but I think you will find that many knife users like a knife whose balance point is located right on the transition between handle and blade. In a folding knife, a bulky and heavy handle will move the balance point back to the midlle of the handle. To me, this simply feels awkward and I therefore would be strongly inclined to regard balance as a part of function - perhaps not the most important one in a folding knife, but still one that shouldn't be discarded without need.
And last but not least there is something to be said for 'neutral' handles such as Japanese knife makers often use for kitchen knives. You could even consider the straight (slightly curved) handles of katanas to be neutral. Neutral handle allow for many grips and fit different hands whereas handles with ergonomic elements like fingers grooves etc sometimes only feel good in the hand if gripped in the preset way.
The last point probably goes beyond the constraints of a discussion of handle to blade ratio but it might show why some of us hope for a straight handle in a Spyderco THO matching the blade (slim blade - slim, preferably straight hande / option No. 2: large handle - large blade). ;-)
But, as I said before, I love my Spydercos, and am quite sure that the THO will meet my requirements, too. Thanks again Sal for offering a dicussion on this.