I've seen soft putters advertised on disc-golf websites and in stores. What advantages does a soft flexible putter provide? I've heard that they "grab the chains" better but what does that actually mean. Is there a physics explanation or is this just all hype?
Grip is a bit of a misnomer, but from a distance that's what it looks like it's doing.
Having a softer material for your putter (or any disc really, but you only expect to do this with a putter) causes more of the energy to go into the chain and less energy back into the disc. The more energy in the disc, the further it's going to go. Either it's going to push the chain out of the way and fly past it, or it's going to hit the chain and bounce backward. Either way, it's going to go somewhere other than where it is - but right now it's hitting a chain, and you'd like it to stay where it is!!
Imagine you shot a ping pong ball at the chain - it would bounce off almost every time (assuming you could hit the thing). But if you threw a pillow, there's a good chance that it would stay.
Obviously neither ping pong balls or pillows are recommend for disc golf, but they illustrate the physics. Soft materials absorb/transfer energy instead of bouncing.
Dave Feldberg recommends a stiff putter (at the time, he was encouraging the use of a KC Pro Aviar because of the stiffness) for the same reason Rob mentioned above - the release.
When you have your putter in your hand, there should be no variance in the flight plate. A gummy putter will succumb to pressure on the top and bottom much more easily (imagine a ripple potato chip instead of a flat chip) and when you release the disc, the natural gumminess will make the disc revert back to its original position, altering the flight ever so slightly.
Granted, if both discs were given the same exact flight path, a softer putter would do a better job of dispersing the energy of the disc hitting the chains better, but you're more likely to get consistent releases with a stiffer plastic.
I like to look at it from a different perspective. I used to use softer putters, made me feel more safe, and less likely of a rollaway. but the release was not consistent. I have switched to a harder putter(of the same mold) and have become a much stronger putter. grabbing chains can be a small benefit, but flight path is more important.
I have a problem with the ping pong ball and pillow analogy. A ping pong ball is light and has way less density than a hard golf disc and a pillow (Even one the size of a golf disc) has way more give than the rubber on a soft disc golf putter. It seems unfair to compare the two. Personally, I use a hard plastic putter and rarely bounce outs other than shots that nick the outside of the chains. However my buddy uses a soft vibram putter and it seems to bounce out quite regularly on the same type of chain contact that puts my hard putter in the basket. At least it seems that way to me. I don't think many pros use soft putters. If that's true then there's probably a good reason why. It would be interesting to get a pro's opinion on this topic.