It's got pretty good range (comparable to f-tilt iirc), is a grab, will hit crouching and very short characters, and comes out a little slower than a n/u-air and at least as fast as a b-air. It's good for stuff like on your backside when b-air would/could be a little too slow, they are too far away to hit with a n-air in front, or they are too low like Sheik's d-tilt or something. It's also nice for when you're not really sure which side of your shield they're going to end up on, since the direction isn't decided until the same moment it comes out so you can switch later on if you need to. To get the full range on it you need to hold towards them during the startup since holding left/right will move you around a bit and get you a little closer before it comes out.
It's more useful with Ganon since his jump is mad slow and the up-b does 17 damage and has better KB, but there's still some situations where CF can't really directly punish them with anything other than an up-b OoS, so as long as they have enough damage so that it's safe on hit you might as well go for it in most cases when the opportunity presents itself.
Some stuff I might find myself using it on:
--Sheik: f-tilt, d-tilt, d-smash, dash attack (if it hits late and they're behind him)
--Fox: u-tilt (they have just enough time to buffer a sidestep, so only go for it if you think they will continue pressuring your shield with another u-tilt or something else), cross up aerials that hit the shield before going behind him, dash attack (hits late/behind him)
--Falco: same as Fox, but also f-smash (late hit on backside)
--Marth: reverse u-tilt (backside), cross up n-air, d-tilt (dodgeable/DDable, so only if there's good reason to think they'll continue pressure)
--Jiggs: f-smash (late hit on backside), cross up AC n-air <-doesn't work, don't do this one lol
--Peach: d-smash (if the last hit catches your shield she can dodge so hold away while shielding to avoid it), f-smash, dash attack (hits late/behind him)
--CF: d-smash, ...f-tilt I guess?
--Samus: f-tilt, dash attack (hits late/behind him)
--Ganon: side-b, f-tilt, d-tilt
--Doc: dash attack, d-smash (2nd hit)
--[Many]: a lot of cross up aerials I didn't mention if they hit high on the shield but aren't quite laggy enough to be sure a b-air would be fast enough or within range to hit them.
