For surprisingly interesting reasons, I've been learning a lot about compound bows over the past few days and it's a fascinating field to study. To the outside observer, most compound bows are pretty much the same, being united in the goal of making an arrow go really fast. When one begins to look under the carpet, though, one sees vast plains of difference between round wheel cams and hard cams, and an archer using a bow with a 7" brace height would call you stark raving mad for suggesting an 8".
Compound bows use pulleys, or cams, to create a force curve that means faster arrows and an easier time holding the string when the bow is fully drawn. In other words, compound bows improve on the abilities of longbows with the only real drawback (haha) being the perception that compound bows are for wusses. On the other hand, while bow hunters may be laughed at by knife hunters, they can all laugh together at rifle hunters, so it's not a bad situation to be in.
I had written about 1500 words on the technicalities of compound bows when I zoomed back out and came to the zen realization that they all make the arrows go fast, and maybe there isn't that big a difference between an 80% let-off and a 65% let-off. All these small things matter, of course, but I'm happy to report that they don't really matter to me anymore. I can move on to composite bows now; I hear it's a whole different target range over there.