I'll get fairly level (so the bubble it at least 50% inside the target bulls-eye. That way the sink & shower drain properly and the dear wife is happy cooking. (and THAT is important, I kid you not)
If getting level means I need to cause a tire to lose contact with the ground, then I retract the jacks and put either 2" or 4" of 12" x 24" planks under the wheel (back up and drive on to the plank) then level again. If 4" of planks won't do it, then the site doesn't work for me. (Very rarely happens)
I echo Mandalay - ALWAYS keep your rear wheels in solid contact with the ground.