I usually use dancing blade for
-Building up general damage(finish with down)
-Getting more space then I probably need(finish with forward)
-Hitting spot dodgers(finish with down)
-Effectively get people into the air with a reliable attack(finish with up)
-Closing in on space and then respacing(finish with any)
-Top of my jumps for the extra vertical height =] when recovering(just the first hit)
-Stopping people from releasing a charged hit/charging hit for a move(dk's punch, another marth's shieldbreaker, etc.)
Hope that helps =] Honestly, just try using it for a few things that fit into your playstyle every so often and it'll slowly grow on you. The most useful part of it is actually just building up some good ol' damage.