Copy / Paste Relative Matrix 
Copy the distance between the selected object or bone to the active object/bone.
Go to a different frame or transformation of the active bone, select the first selected bone and paste.
The object/bone will move into the same distance from the active object.
This can be used instead of constraining bones, especially during animation blocking phase.
Paste To
- Current Frame - Paste the matrix only at the current frame.
- Selected Keyframes - Pasted to all the selected keyframes, also the handles will be adjusted to match the matrix during the inbetween frames.
- Frame Range - Pastes and bakes into a custom frame range.
Using the markers range, it's possible to use the markers as widgets to setup the custom frame range, instead of entering numbers numerically.
Selected Keyframes
Copying the Hand relative to the hips and pasting it to the selected keyframes
Tip
Instead of dealing with constraining objects to bones, use copy relative matrix over a frame range or selected keyframes.