^I used it once, but it was over a year ago now. From what I recall, besides allowing the option to take characters down different paths at the beginning, it made it easier at different junctions along the way - it was very handy bouncing Yuna and Lulu between white and black magic [especially improving Magic for Lulu, as the magic nodes are more prominent on Yuna's side], and Wakka was my real powerhouse when alternating between his and Auron's areas. You'll have less nodes to play around with overall - but not an awful lot less, and only insofar as you are attempting to gain maximum HP, so it's not that big of a deal.
Since you've played the game already and have a good feel for it, go for Expert then if you like the idea of switching between paths more easily - you can get some useful abilities sooner using other character paths or have other characters not restricted from learning other abilities - for example, Auron can get Tidus's haste as there is no Lock in the way. [And from what I see online (though I can't recall from my own experience), you'll finish character paths sooner if they do not deviate]