Just to expand on Hal's point a bit more...

The frame becomes stressed unequally side to side when the tires lie on ground which is not level, latitudinally, and then the corner stabilizers are used to level out.  There has been discussion in the past about first achieving a basic cross-trailer leveling by using blocks under the tires.

One should have the wheel suspensions [equally] bear a significant portion of the trailer weight to minimize frame flex and its wierd effects.