Without getting into the details of how the guide works (you can find that info at the link above), suffice it to say that the honing guide provides a way to maintain an absolutely consistent angle between the stone and the tool's cutting edge. This eliminates the possibility of a rounded bevel. After honing on successively higher-grit stones, one can easily achieve a mirror-finish on the cutting edge and on the tool's flat back. Many people overlook this last point: Unless the backside of your iron, chisel, or machine knife is dead flat, the sharpness of the cutting bevel is basically irrelevant.
I've also been reading about and experimenting with different stones. I've tried a variety of oilstones (both manmade and natural), waterstones, and the relatively new 15- and 5-micron grit mylar-backed abrasive sheets. People can get very passionate about the benefits of this-or-that stone, but I'm convinced it doesn't matter a whole lot what one chooses as long as one starts with a fairly rough abrasive and ends with an incredibly fine one. Also, there's no reason, despite prevailing norms, not to go ahead and mix up different kinds of stones in the honing sequence. To wit, I'm now beginning with coarse and then fine India (both oilstones), progressing to black Arkansas (also an oilstone) and finishing with an 8000 grit japanese waterstone. This produces a chisel edge that can not only shave the hair from my arm, but even the stubble from my chin. Yes, I tried it!
If I'd been able to sharpen tools this effectively 15 years ago, it's hard to calculate how much fretting and gnashed teeth I might have saved myself.