Jack stands are almost useless without the load on them. If you leave the weight n the jack chances are if it was to fall off the jack it would roll back and miss the stands, or if you were under it in a panic jumping up if you saw it ready to fall you could easily hit the stands and knock them out of the way. You want to lower the weight onto the stands. I usually do tat then tighten jack back up and jack it up just enough to touch the load. Most of the weight should be on the stands to keep them in place.
