Beading up is just a visual indicator of surface tension. The more easily a liquid beads up, the higher its surface tension.
Is beading up useful per se? Of course not, no more than suds and bubbles. But in RRL it's an indicator that surface tension has not been reduced to a level that impairs removal of the liquid by vacuuming. Fluids with excessively low surface tension (ie, that don't bead up) adhere so closely to the record surface that they cannot readily be vacuumed away.
Is beading up useful per se? Of course not, no more than suds and bubbles. But in RRL it's an indicator that surface tension has not been reduced to a level that impairs removal of the liquid by vacuuming. Fluids with excessively low surface tension (ie, that don't bead up) adhere so closely to the record surface that they cannot readily be vacuumed away.