Straightarrow, I'll try to explain. It's one of those things that is common knowledge among guys who make homemade traditional or primitive bows, and it translates equally as well to compounds.

Most guys set their tiller even at each end of the riser and call it good. That'd be fine if the handle was centered in the bows' risers. IT'S NOT! The throat of the grip is a couple of inches below center. Several inches on some bows. Someone using a low wrist grip puts the main pressure of their grip a couple of inches lower than the throat. Visuallize the bow's riser as a lever and the grip as the pivot point. The pivot is offset five to six inches.

That naturally puts more strain on the bottom limb to begin with. The limbs will be unevenly stressed when the bow is drawn.(Instead of 35 pounds top and 35 pounds on bottom to make 70 pounds, you wind up pulling more like 30 pounds on the top and 40 pounds on the bottom to get your 70 pounds of draw. Somewhat exaggerated but that's the idea.) The limbs will deliver uneven thrust when the shot is released. Nock travel will certainly not be 'straight and level' even on a 2-cam bow.

You note how one limb can be made to jump forward more than the other limb as the bow returns to brace during the shot. That's the effect I'm talking about. Ideally, the bow should be tiller adjusted to suit the bow's grip location and the archer's shooting style (high wrist, neutral wrist or low wrist grips put the pressure in different locations in the handle). This will allow both limbs to be under equal stess during the draw and shot and the limbs will return to brace at exactly the same time. If it has not been adjusted properly, the bow will have one limb slamming back to brace before the other. That's what makes one limb kick forward more than the other.

Naturally, this is going to cause more shock, noise and vibration with one bow than another. For instance, try shooting a longbow that isn't tillered properly! WOOF!!! That handshock will run right up your arm to your jaw and you'll swear you had a couple of teeth swap holes.[:-]

It won't be as obvious with a compound as with a longbow, naturally, because of the much greater mass in the compound riser. Among compounds, it's not as obvious with a long riser bow using short parallel limbs as it is on a bow using a short riser and long limbs with conventional limb angle. It's not as obvious, but it's still there. And regardless of what one high end bow manufacturer claims, it's just as present on single cam bows as it is with duals and hybrids.

I set my tiller even to start out. Then I point a pin at a spot on the wall and s-l-o-w-l-y draw the bow straight back. The bow will try to pull the pin up or down. For me and my shooting style, it's usually up. I take a turn off the top limb bolt, add a turn on the bottom limb bolt or both. (Naturally, if the pin is pulling down, I'd take a turn off the bottom limb, add a turn to the top limb, or both.) Then I repeat. I keep doing that until I can draw the bow all the way back and keep the pin from rising or dropping during the draw.

That tells me I'm putting the same amount of energy into each limb during the draw. Which means I'll get the same amount of thrust from each limb during the shot. Which means both limbs will return to brace at practically the same time. Which minimizes shock and vibration, and minimal vibration means minimal noise. Which also means you aren't wasting as much energy on shock and vibration, so where does that energy go? Seems obvious to me the energy has to be going into the arrow!

Also, having the limbs draw equally means the limbs won't be fighting your grip to equalize the poundage difference when you're at full draw. Which means you'll be able to hold aim much steadier on the target.

From my point of view, the ability of being able to easily adjust tiller is one of the compound's major advantages over traditional bows. In fact, I put it's importance second only to let-off. So many benefits, but so few people actually taking advantage of it.