It's intended to offer a similar result,
in theory, as the floating brake design (not to be confused with a car's floating disc brakeOn a single pivot design, there's just the one pivot and link (swingarm or wheel link) controlling the movement of the rear axle. On a majority of those single pivot designs, the disc brake caliper is anchored to that link/main swingarm and,
in theory, the forces that go through it under braking can affect the suspension significantly. You can't normally put the brake on the seatstay if it pivots, since it won't follow the movement of the axle, which the rotor also follows. A floating brake caliper design you see on some bikes, like the older Konas, anchors the caliper on another link, and to a link that follows the axle, with the braking forces being transmitted to the link that doesn't move as much, as opposed to the main swingarm that does move a lot. On the ABP and Split Pivot, the brake is moved away from the main swingarm, and since the concentric pivot means that other ar
A lot of brake jack is unwanted, since when you hit the brakes, your weight shifts forward and up, in a similar direction as brake jack, which ends up wanting to throw you over the bars. In reality, most single pivot bikes don't have brake jack. They have what's considered brake squat, or brake anti-rise. Having a decent amount of this is desired, as it can balance out that forward weight shift when you slow down. In other words, brake jack is a myth. I'm not declaring myself to be an expert at this, but I at least know that those who dramatize brake jack don't really have much of a clue. There's a lot of happy people on single pivots these days and it's not because DW made it cool with Split Pivot...
P.S. Beware that the "chainstay" isn't always the main swingarm. For example, the Devinci Wilson has a high pivot and its main swingarm is what some may consider the seatstay. In this case, the brake is put on the chainstay to get the floating brake effect.
In this, it shows that the Yeti has brake squat
throughout its range of travel. The Bronson, however, has less brake squat and is more susceptible to forward weight shifting the deeper it is in its range of travel. One can interpret from that that to compensate, the rider on the Bronson would probably be more behind the saddle and lower to counter that force, while the Yeti rider would more comfortable in a balanced and neutral low attack position in comparison. Doesn't show that either suffer from some major flaw that makes them unrideable; but it may teach you more about your bike and how to ride it optimally, by knowing more about it. I've browsed quite a bit of that site and I can't say I have seen a design that was really questionable besides the Zerode, honestly, but I can't really say it's bad, just unusual.
TL;DR: brake jack is a myth, floating brakes aren't needed, and I don't know enough to really say if its more than theorized mumbo jumbo or not, but I suspect that it really doesn't offer as big of a benefit to a rider as they hope that you would believe. I can say that it at least offers them, as designers, more control over the suspension to get a balance, or better compromise, of all the characteristics that they want a bit easier.