Regarding the vidéos posted by JeremyH and fiol lately, we can again start to debate on HD Mode usefullness.
You can see in this videos that Iori, Kyo and Yuri use HD combos. Especially Kyo.
I think using HD Mode or not is really conditionned by the character you are currently playing. I guess Kyo don't have a good use of DC so it's better to use the HD meter for HD mode.
The other HD combos we saw are really situational, the player open opponent's guard with jump or light attacks and have a full HD meter. He is able to launch an HD combo from their and this is what he is doing.
For Takuma's case, HD mode is not very usefull as his corner combo using Zanretsuken to DC Kyokugen Houken is so powerfull that it is usually enough by itself to deal massive damage. Not to mention that Takuma is able to build a lot of meter this way unlike HD mode combo wher you don't build meter at all.
For Elisabeth, she barely doesn't need HD meter at all but can come in handy when she has no Super meter.