Full and Split change who speaks each line, never how often you hear it. In Full mode every voice speaks the whole script: a chorus of complete layers, at a cost that scales with the cast. In Split mode your voices share the script between them: every line covered, voiced once, for a fraction of the credits.
The repetitions are identical either way: eight voices cycling one-eighth of the script each repeat a line exactly as often as one voice cycling all of it.
Which to pick: Full when you want the denser chorus and the credits allow it. Split when the script is long, the cast is large, or credits and time are tight. Because the repetitions match, Split gives up nothing you can hear; it only means one of your voices speaks a given line instead of all of them. On Budget voices the choice also decides the waiting time, since Full makes each voice render the whole script in turn.