The uneven settings are just to create more stereo effect. It is not necessary and you can just as well set pitch to -10 and +10 or whatever. Or have no delay at all. Or use just one pitch for a mono sound. Just play with the setting and use your ears. There are no rules. Setting the pitch to small intervals create a chorus like effect. If you want a more extreme chorus like sound with more wobble set the pitch to +20 or higher.