</font><font color="blue" class="small">( almost everyone here mentioned mowing with the back of the mower higher. )</font>
The original intent was to have the major work done by the front hitting heavy brush/weeds/saplings and not having a lot of contact with the rear to relieve some of the work on the gear box, etc.
In high, thick material, having the mower level or the rear lower than the front will result in a poor cut and more stress on the system. With the front higher, the tall stuff is going to get pushed down some by the stump jumper before the rear can cut it, for one thing.
Having the mower level or the rear just a bit lower than the front on lighter material is a good trick for replacing a lawnmower. It's not terribly stressful to the system, and gives a pretty good cut, but for the thick, heavy stuff, the front should be a bit lower.
If one doesn't want the stuff thrown out the rear, it's best to but chains or a flap to help slow them down rather than to have the front higher to avoid it. That stuff being thrown toward the tractor can cut/puncture tires, dent/break tractor compenents, and with many tractors, hit the driver.
John