Basically you can use it to space and bait people. Seemingly mixes somewhat well w/Platform Canceling, too.
You seem to have enough time to do the following out of it:
N-air
Charge Shot
Homing Missile*
F-air*
U-air*
Screw Attack(lol aerial Up B)
Z-air
Another Morph Ball Bomb*
*means I either don't see much use in it, or am not sure if it's possible.
I'm getting the hang of doing it consistently, but I can't really explain how to do it well. You need to do the Spider Ball(Down B immediately off a ledge to descend) off a low platform(I used BF), mash the control stick(This is where I'm really confused. I'm not sure which direction. At first I thought it involved jumping because I had tap jump on, so I just mashed up. Since then I used a config not involving tap jump and was still able to do it, as well as mashing left and right as opposed to up), and sometimes you'll float back up, sorta like "bouncing," though it's only a few feet off the ground as opposed to a full or maybe even a short hop. I want to keep messing around with it and best case scenario, find a way to do it without the need of the Spider Ball/platforms and a way to do it more than 2-4 times in a row without messing up.
tl;dr - Don't get your hopes up. I see this in kinda the same light as that sliding grab thing Xyro discovered a while back, atm.
Edit: Hella harder to do because of the moving, but I just did it on SV.