Well, it's probably a necessity. First, that saw blade doesn't look long enough to get a enough action to cut a man in half like that. Even if his legs were apart and you only measured from head to hole, there's still probably not a while lot of room to maneuver the saw which is gonna make this grim work even worse: it's also gonna be hard.

Second, it's gonna be harder because you have so much blade in constant contact with your material. I mean, you're not gonna cause any saw burns or nothing, but you're definitely gonna piss off your saw bois. This was a time before power tools and friction makes you sore.

Now I'll admit it's gonna be harder to keep a straight line all the way down, but we had already talked about the need for a clamp, so why not set up a fence alongside it? I mean, if we're optimizing we might as well go for quality, too.

Hell, might as well go all the way. Drag the whole setup out to the mill and (assuming this isn't already a saw mill) build a contraption that reciprocates the saw using the mill to power it. Now, not only do you have the means to easily cut a man in half, you then also have a saw mill.

I suppose, too, it could act as a deterrent for future... Um... What was the condemned is guilty of? Sex out of wedlock? Stealing bread?

Oh! We should put a conveyor at the start of it! I bet we could strap a whole sinners' family to it at once!