The Standard Grid leads each character along a very specific path, and it's very hard to stray from the "right" path for that character, as opposed to the Expert Grid where I've known people to suddenly send Yuna down Lulu's route without really noticing what they were doing until they noticed she had a full set of 'ara level spells instead of Cure, Protect, Shell and Reflect*.

*"Mirror of light, reflect magical spite!"