I've taken a look at most of the tutorials out there for rigging, and I've found only 2 tutorials that actually make somewhat of an effort to explain the advanced twist controls for Spline IK.
Those being DT's Cartoon character rigging and JS's AFR series.
They're both great, but they don't cover these options in enough detail.
Check the image below.
I can use a variety of combinations as the UP AXIS/UP VECTOR and still get the same result. Can anyone provide a bit of input on these settings?