I guess it would only work if there's not a long CD on Slowfall - which I don't know - never had to cast it quickly on myself multiple times.
HALO - High Altitude Low Opening
As a mage - I know I can fly up on a flying mount, dismount - then Cast it on myself.
Imagine a raid on a location in Northrend where you don't run into the location through the guards - You literally fly so high no one can see you, Time your dismounts - then cast it on everyone on the way down.
The fall is several seconds from the highest point.
For a 5 man group - Assume tank, Healer, DPS, DPS, Mage - time your dismount - All at same time.
1. Slow Fall DPS
2. Slow Fall DPS
3. Slow Fall Healer
4. Slow Fall Tank
5. *ALT Slow Fall Self*
(Mage has to be last to slowfall - otherwise the group would fall faster away and be out of range)
You want the Tank on the ground as soon as possible - so you let him fall with the mage the furthest....
Imagine a raid doing this?