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.
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.