I've seen a few posts here and there and it struck me that there seems to be some confusion with some about what exactly it is that adjusting an "adjustable" razor does. I've heard it refered to as "blade exposure." I've seen comparisions to lawn mowers and not dropping the deck all the way down, etc...
So in the interest of helping to clarify this, I'll try to give a good description of WHAT exactly the adjustment does.
In an ideal world, where your technique is flawless, your hand is steady, and you can factor trigonomic values with eyesight alone like the 6 million dollar man, the adjustment does ABSOLUTELY nothing.
Why? Because the safety guard will never be touching your face anyway. It won't matter if you set it for the lowest or highest setting, or remove it completely, the results will be exactly the same...
Now for the rest of us that aren't bionic, our hands are far from that accurate. That means the safety guard is going to come into contact with your face. That is after all what it's there for.
Let's take an adjustable razor like the Vision by Merkur. When you adjust it, it does not change how much blade is "exposed". It does not bring the blade any CLOSER to or FARTHER from your face...
I'll say it now... The blade will ALWAYS be in contact with your face, not close to, but IN CONTACT WITH.
What the adjustment WILL do however, is RAISE the head of the razor in relation to the safety bar. In other words, the "Gap" between the blade and safety bar get's larger.
This changes the ANGLE at which the blade is contacting the face (Assuming the safety bar is in contact with your face.)
Let's take a look at this with pictures. (Excuse my poor photoshop skills.. ;)
Here's a picture of a razor with the adjustment set at the "least" agressive setting. Dialed "down" in other words.
The vertical line on the left represents your face. The "red" is the razor blade itself. In the close up on the right, you can see the yellow angle that represents the angle of the blade to the face.
Now as we open the razor up, to a more "agressive" setting, the head will "raise" giving more gap between the safety bar and razor. This will force you to have to have LESS angle in order to keep both the blade and safety bar in contact with your face. (For demonstrative purposes I've exagerated the amount of opening of the head) This is a razor in it's fully open or dialed "up".
Now you can see to keep both blade and safety bar in contact with the face we've had to lower the angle of the handle. This in turn increases the "angle of attack" of the blade itself, again represented by the yellow angle.
If we superimpose those angles on top of each other (and change the color of one to keep clarity)
We now see that at the "less" agressive setting we've ended up with a fairly shallow angle, while the "more" agressive setting resulted in a much larger angle.
Now as stated above, if your the 6 million dollar man and have the razor at the most agressive setting, you can still keep the handle at the same angle as previous, that in turn will keep the angle of the blade exactly the same as well. The safety bar in that case would be lifted completely off the face and would be serving no purpose at all. (might as well be using a cutthroat).
You'll notice that in NO WAY does adjusting it change the "amount" of blade that's exposed. Nor does it ever "prevent" the blade from contacting the face. Your not setting how CLOSE of a shave you want, rather your setting how "Agressive" of an angle the blade can potentially be in reference to your face.
That's about all I have to say about that...