First example that came to my mind: You respond to a high risk call and confront a suspect who appears unarmed. He appears unarmed or perhaps drops a weapon. He refuses to obey further commands, tells you that he's going to kick your butt, and escape. He advances on you.
Granted, he could attempt to disarm you which would definitely rise to the level of deadly force or he could be too big and bad for you to handle. On the other hand, you might be able to deal with the miscreant using the miracle of electricity, the power of cayenne pepper, or even your willingness and ability to roll around in the mud and the blood and the beer.In this day and age (well, any day and age), I'd rather cuff someone up without shooting if reasonable. That said, I'd rather have the option of holstering up quickly and going hands on or using a less lethal.
When you have a holster with an ALS, you have the best if both worlds: fast on presentation, fast on holstering.