Hmm... I will say, while dash dancing is useful, being able to smoothly transition from fox trotting to dash dancing and vice versa is way more important than dash dancing on it's own.
In most circumstances, the goal is to keep proper spacing (being near or just in the opponent's "burst range" or the range at which they could hit before you could react) in a manner such that you have solid retreating options. The reason you want to be close to the opponent is so they don't steal space from you (being near the edge is bad since you don't have room to retreat). The reason you don't want to be in their burst range is fairly obvious, you don't want to get hit. The reason you want to be able to retreat is so you can dodge attacks and then come back and punish them.
So the problem really, is that when you go into a run, you can't turn around quickly, making it both hard to maintain proper spacing, and hard to retreat when need be. Thus you fox trot, or flick your joy stick in the direction you want to move (just flick, don't hold), and then re-flick the joystick after the dash ends if you want to continue in that direction. The weird part is, you have to time flicking the joystick to go the same direction twice (fox trotting) since you have to wait for the end of the dash, but you don't have to time flicking the joystick in a different direction than you just went (dash dancing).
That all said, dash dancing does have a use on it's own, but you have to understand when and why it is useful. Dash dancing is particularly useful when your opponent is in a disadvantageous position such as being near the ledge or being in their shield. You want the tip of your dash dance to hit or slightly intersect with the tip of their burst range. The goal is to make them feel like they can't tell whether or not you will actually approach. Typically you want them to take the bait and try to hit you which you then dash away from and dash back to punish. That said, you can get a feel for how timid or hasty an opponent is in this situation, and if they are timid you can push further into their burst range -> retreat to see if they took the harder bait (if so wait and then come back and punish) and if they don't react, you can go in. You can mix up how you decide to approach, but personally I think it works best after the person fails to go for a hard bait from you, since you are already closer than usual to them, making it harder for them to react to you going back in.