These dies are for use on progressive presses. It is in fact relying on the powder drop to either dump it all or dump none of it. It is the suspenders to belt and suspenders. For me, it is something I put in place once I started getting a lot of crimped primer brass in 9mm. It'd hit the priming station, I'd have to deal with it, sometimes I'd overly focus on remediation and wonder if I had re-indexed everything properly, and be both paranoid and delayed dealing with it.
IMO, unless dealing with REALLY compact powder in a big cartridge, it'll stop double charges, no charge, and for some cartridge/charge combos catch it if you substantively sling powder out of the case in a progressive.
The other reason to go with one is ergonomic. lock out function aside, it and the hornady powder cop let you replace looking into the case with watching a rod move up and down. Because I find the lock out die does not work very well with .223, I use the powder cop there. It's a pain in the ass, even with a good press light, to see the powder and make a determination on how full it is. And with rifle, you have a long powder column. So if it's less than 50% full, it doesn't move. With my powder selection, there's not enough room to overcharge the case without seriously impeding seating. A double charge will make a huge mess. So it's good enough.
Prior to using the powder cop, I've gotten a couple of squibs. Since going to it, I've had none, and it has caught a couple.
Another benefit, at lest for my LnL-AP, is that it catches it earlier than my eyeball. Due to the shape of the press, without it I go size->prime->powder->nothing->seat->crimp. And you can't apply the old mark 1 eyeball prior to where I seat due to the press support. When it does catch something, there is one less case with powder to deal with, and simpler remediation is always better. It's harder to screw up simpler.
Another benefit beyond that, at least to me, is that the mechanism tamps the powder down. With flake powders, I find that depending on how the flakes fell, stack, and bind, there can be significant variation in the visual appearance of a correct charge. The mechanism of the lockout die tamps it down a bit and makes visual presentation much more uniform. Which makes my visual check more effective. No more tapping the occasional outlier that looks overly full to see if it settles or not. Which speeds things up.
I've got over 120k rounds reloaded. I've never had powder stick in a drop tube, much less stick and drop free later. I suspect that is because anything that might do that will meter like crap and self-selects itself out of contention as a usable powder.
What you can use it to protect against varies greatly with the powder in use. But for me, I always adjust it so that it is just shy of locking out from overcharge with my actual intended load.
As a note, adjustment should periodically be verified it can drift a bit over time, especially if you adjusted it to the ragged edge of locking on your expected charge.