I'm no expert but seeing as you haven't had a reply yet from one who is I'll take a shot. If we number the points you've circled from the top down, I suspect it works like this:
1. Crank adjust is the primary height/depth adjustment.
2. Appears to adjust the height of the wheels that help carry the weight so it isn't all hanging from the 3pt.
3. Rough height/depth adjustment, fine tuned with #1.
4. Moves the wheels fore and aft.
5. Positions the dirt shield up or down allowing you position it properly relative to #1 above.
6. I can't see it well enough to guess.
Now as to why you would want to play with those adjustments varies. For instance, positioning the wheels farther aft would tend to lift the tiller over sharp drops in the lanscape thus leveling somewhat. If you haven't already, play with it and see what makes sense to you.
