I have seen some people do this, and I know the rules that you can't do it inside of 30m, but why do it at all? I don't see a reason for it.
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I don't jump putt, I use the Fedberg/Nikko tactic of following through with a step, i.e. "Chasing The Disc Down". It works sometimes, but certainly not always. Most people who do a true jump putt miss....even the pros.
*shrug* I don't know anyone who consistently drains 75' putts, step through, jump or standstill. Just sayin.
http://www.youtube.com/watch?v=xZWTGSy_EC4#t=0m44s
The theory is simple and actually comes from ball golf.
If you can putt, do it. You have more control with a putt and are more likely to get the ball or in this case the disc closer to the hole or basket.
The jump putt allows one to increase the range of the putt.