Avoiding accidents.
I can pull their tubs open, which avoids them shooting out and grabbing me or anything else. I can redirect their attention if they're keyed up. I can pick them up, move them around without getting tagged. I have both my snakes hook-trained so they know when they are being fed and when they are being handled.
My BP has recently become a very aggressive eater - he knows when he's being fed and he WILL come flying out of his tub to get his rat. I can use the hook to make sure he actually gets the rat.
I'm not afraid of getting bitten. Been there, done that. I've had worse scratches and bites from my cats and dogs. However, I have seen snakes with abscessed teeth - snakes that got abscessed teeth because their owners had a very natural reaction and jerked back when their snake snapped at them. It was an accident, and a costly one.
There's a multitude of reasons, really, but they all come back to avoiding accidents.