Dtilt is primarily used for tilt locking characters at 0%, but after 45% or so, it's function is no different than SH Uair and Uthrow/Fthrow. Still, it's a fairly fast move, being Frame 6, and if you're having trouble getting the grab or Uair, Dtilt can be used.
Homing Attack doesn't really have an appeal to the point where it's "Use HA for this situation." It's a last resort for recovery mostly. But I do find use for it on landcampers who are just itching to grab me on landing. I lost count on how many times I've had Dair -> HA work because of it.
Usmash beats airdodges, and has invincibility + high priority to beat aerials, but it will never kill, and if anyone knows how the move works, it's going to be DIed. It;s best used as a Hyphen Smash for an "out of the blue" kind of attack.