In Vanilla MvC3, the purpose of the DHC glitch was to reset the damage. In Capcom games, damage tends to scale down the longer a combo goes. You could sidestep this by doing the glitch. One character does a super, and then another character DHC’s with something that doesn’t hit, which resets or put the combo damage back to normal, unscaled levels (and being able to continue a combo with “normal” damage).
Commonly used for these are Magnetic Tempest/Elemental Fury into stuff like Wolverine’s Berserker Charge or Wesker’s super counter.
Examples at 0:28 and 1:20 of this video
and 0:26 in this one (sorry bout the quality)
In Ultimate, I believe it refers to something different, one of Nova’s supers when the game was fairly new.