I personally find lots more applications to Cantata, rather than Fermata.
I only see (3) reasons to use Fermata.
1: early in a combo for big damage
2: at the end of a combo when you know the 100 dmg difference over Cantata will kill
3: Air UB, which currently has no set-up for. =(
Cantata applications:
100 less dmg to fermata, but allows a kd/ok set-up.
long combo... Cantata, 8]D[, IAD, J.2C, J.B, 2]D[, Cantata, 8]D[ for great damage
react to burst... Cantata
Corner UB set-ups w/ tension No ada... Cantata, RC, 66, 6[C]
Corner UB set-ups w/o tension with Ada... Cantata, 22]D[, 3]D[/J.C or Cantata, 22]D[, 2B, 3C+2]D[
Blowback forces opponent into corner
Midscreen UB set-up with Ada & 100% tension...Cantata, Fuoco, RC, 6[C]...
Corner UB set-ups with 100%... Cantata, RC, JB+C, 8]D[
Can be used to Yomi against Counter Assaults/reversals.
If you mes up the summon combo and ADA is all the way across the screen use this time to WALK YOUR BITCH, also be sure to input VIVACE as soon as Cantata is finished to allow the screen to catchup with ADA's position as well.... 3C, IAD, J.2C, Alle~can, 6A, Cantata, 8]D[, IAD, J.2C, J.B, 2]D[...
With on-line play, it's kinda funny how often the last scenario has saved my ass.