Re: jack plates...
On every boat there's a "sweet spot" for any given propeller. The setback helps you find that spot. It also, as mentioned, changes the fulcrum point which can add bow lift. Setbacks are anywhere from 3" to 30" or so. Lots of options. The theory is that the further you go back, the higher you can raise the motor. To a point. Walleyehed can tell you what appens when you go too far.
Then there's the advantage of running in shallow water. Most flats boats have hydraulic plates. You can run the plate to extreme heights and get over a flat. Or raise the plate up to take off in shallow water.
Basically lots of options, lots of reasons, lots of styles.
