The Rotation option lets you paste and match a pose to the rotation of the selected object.
Pasting with the Rotation (R) option active A. In the pose to be pasted, the selected Hips effector is oriented at an angle from the camera B. The character the pose is pasted on faces the camera C. The pose is pasted and the character assumes pose A, but keeps its original orientation, facing the camera
When pose A is pasted on the character in B, the orientation of the character in the resulting pose (C), is based on the rotation of the Hips effector in B. The character assumes pose A, but retains the rotation and translation of the Hips in pose B, still facing the camera.
If the Mirror option is also active, a red indicator displays on the selected effector to match, indicating that the mirror-pasted pose will be based on the rotation of this effector. To hide the red indicator, disable the Mirror Visibility option.