Assuming you're talking about a real beading tool, and not the scraper-with-bead-shaped-cutouts tool...
Beading tools are designed to make beads. You use the edge just like you'd use the skew's edge, but in theory, the geometry of the beading tool's shaft helps you roll the bead more easily, if the bead is the same size as the shaft. I often use my parting tool as a tiny beading tool this way.
Think of it as a short fat skew that isn't skewed ;-)
The scraper-with-bead-shaped-cutouts tool is for when speed and consistency are more important than surface quality, or for people who haven't mastered beads with a skew and would rather do other things, but need beads anyway.