Matthew,

Bear in mind that what I say on this subject is merely an educated guess.

The dropped choil is probably a feature influenced by the forging process. While some forge blades and prefer the blade to be in line with the ricasso, it seems to me that the act of drawing the bevel down just appealed to some makers and it has stuck around. It's easier to pull it down than to take it anywhere else. So, I think the act of forging influenced the development and acceptance of this feature.

As you mentioned, it does demarcate the back of the cutting edge. Depending on the guard, it might also make the edge easier to access the sharpening stone.

The dropped choil is not a necessary feature for a good knife but, in my opinion, has become a design feature as much as anything. I use it sometimes as part of the securing system within the sheath.

Some design features of objects are there because of influences long past and of which we now know very little.

Here is an example of how a simple shape has been influenced by a number of factors, most of which are long forgotten.

In the above picture, there are two skeleton keys. The one on the left is forged in the old way. Really old. You can see the lap of the scarfs where the ring was closed and forge welded.

The other key, while old compared to us, could be much later in time because it is cast. But see that the shape is generally the same with it's "peak" pointing in. It's not necessary to have that feature in the cast key but that is what looks familiar and what would be expected.

Matthew, The choil, whether dropped (as in the upper knife) or a cutout (as in the lower one) aids in the sharpening of the edge only in as much as it allows you to get all the way along the edge without butting into the ricasso. When using a stone or steel or strop, getting all the way to the back of the edge is going to get the ricasso scratched up unless you separate the edge from the ricasso. Providing a space, either behind the edge (choil hole or notch) or above the edge (dropped choil)aleviates the possibility of running the sharpening tool against something that you don't want to sharpen.

Thank you for your explanation Mr. States,that makes alot of sense.

Thank you so much guys! Makes perfect sense to me now.