1. Higher flash output
2. Don't drain camera batteries
3. Greater control over flash output e.g. fill in 3d balanced
4. Bounce flash
5. Control over direction of flash through swivel head
6. Faster recharge rates
7. Superwide angle coverage
perhaps every-day situation is a better word.....by usual, I mean situations like low and white ceiling for bouncing, use as a fill-in flash, when the subjects are near (not like 10-20m away), etc.
If you need bouncing onto very high walls, want to illuminate people far away using flash (e.g. during fashion shows where you have to stand a good distance away from the runway), attach a flash extender to shoot birds, want to bounce onto walls, etc, you need a stronger flash.