It gives your bow better early draw tension, since you have to move the tips of your limbs further to brace it. That gives you a better force draw curve, which means you are storing more energy. Storing more energy, in theory, means you get better cast for the same draw weight.
In theory, and there are a lot of variables, a set back accomplishes the same thing as reflexed limbs or recurves. It might be easier to just bend the bow once at the handle than twice at the tips or over the whole length of the limbs, and you wouldn't have to worry about making the bend match on both limbs.
I've made a few, and they turned out fine, but remember, any of the above options stress the limbs more than a straight stave design. If your design is pushing the edge of what the wood can do, the bow is more likely to fail.
