Super Fang seems most useful to
1. compound residual damage or
2. ease prediction.
3. ruin walls
As someone pointed out, if you can hit something with Super Fang then KO with a move you could have 2HKOd with that same move in the first place (unless it's brine).
However, if you aren't sure what will switch in and thus what move will get you the 2HKO, Super Fang can be a nice catch all that will allow you to take the right follow up action once the pokemon is known and sits at 1/2 max HP.
Crobat will seem to work well with either points 1 or 3.
It has the right typing, offences, and speed to force things out, Super Fang the switch-in, U-Turn out to a counter and rinse/repeat while switches get punished by hazards as well.
And as mentioned, the Taunt/Super Fang combo works against walls with Crobat being fast enough to Taunt or trap opponents with Mean Look before they can run.
The problem with the combo is that if you retain roost you won't have a reliable damaging move.
Though Super Fang can beat anything in roughly Log2(current HP) + 1 Power Points since it'll do the 1 HP damage to finish.
I might be off because I'm not sure how the game handles odd HP values (at 5 HP does it take away 2 or 3) but it seems like a reasonable estimate.
So you'll be using ~ 10 PP (without PP max) to beat a full health Max HP Blissey at lvl 100 and ~9 for Hippowdon.
Leppa berry much?
I guess I have my doubts about the wall breaking trapper that lacks a reliable attack but Super Fang definitely boosts the scout Crobat.