Every time I see this sword I think of Richard Lester's The Three Musketeers, in which D'Artagnan , played by Michael York, is given a rapier with this special feature.

[a scan fom A.V.B. Norman's book Arms & Armour]

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Saw a very similar rapier in the Töjhuset armoury in Copenhagen, Denmark. Neat little trick, that.

I'm curious though, other then as a novelty what use would this thing have?

I hate to bring hollywood in to this. But these screencaps help illustrate Björn's idea.

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It need not be so dramatic either. Once you are inside each others point you end up grapling and if you have control of your sword you will have an opportunity to use a classic back handed or reversed grip in your favour. From what I understand such "gimmick" swords would have been created because there was an apparent use for them.