Dash attack is a very good surprise move, I find. It comes out fast out of a dash and has a decently large hitbox. I've gotten actually quite a few janky kills from surprise dash attack -> jab reset -> knee. It is kinda good at high percent against spacies/falcon in that any solid hit at high percent is good against spacies/falcon and dash attack is, again, a really surprising move to bring out.
Having said that, it has it's downsides. If you whiff or don't get the initial strong hitbox, you're usually a sitting duck for almost anything, and getting grabbed -> combo'd is the last thing you want to happen against someone who's at high percent lol.
Weak dash attacks at high percent might knock 'em down, which can lead to tech chase or jab reset stuff. Strong dash attack has good knockback, but the cool-down afterwards prevents a lot of reliable followups. Of course, if they don't have a jump, then GG's.
Dash attack has a lot of potential for edgeguarding IMO, especially against falcon. More for its hitbox than its speed, because it actually hits pretty low and can cover sweet-spotted up-B's (i think). Also, dash attacking at the edge puts you in teeter, so if you hit the dash attack, you kinda can follow up with almost anything at that point lol