What is the DefualtMethod override for the pose driver?

I set up the pause driver and originally expected the default 0th to be 100%, but it is not.
I set Override to Quarternion and the 0th is now 100%.
What does DefaultMethod actually do?

check source bone, check whether source bone only drive several bones, and check the rbf parameters of the fbx you import, the rbf parameters in pose driver should be same as the animation in MAYA

I figured it out!
Default method means the setting I setted at the Distance Method under RBFParams.
The default method of Distance Method is “Swing Axis”. So, in most cases, Default Method in Pose Targets is equal “Swing Axis”.
Thank you

Thank you for providing me with information.