None whatsoever. You can play the entire story mode from Dissidia in Duodecim.
Also Prologus was apparently this downloadable thing with a little story segment and a few characters. Aerith is merely an assist character, and unless you really love her and really hate Sephiroth, Kuja or Jecht, that shouldn't be the major reason for getting Prologus.
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SomeC - sheer explosives since meeting that crazy hobo.
BlAcK TuRtLe grabbed the Guru victory, slow but steady.