The Snap Constraint to Bone button seems to only rotate and change the limits on a constraint instead of also moving the constraint to the bone's location.
Steps to Reproduce
Create a new project based off of the Third Person template
Open the Mannequin's physics asset
Change to "Constraint" mode
Select the Constraint on the Mannequin's shoulder
Move the constraint away from it's current position
Press the "Snap" button on the toolbar
Result: The bounds of the constraint change and it rotates, but its location is unaffected and it is not moved back toward the bone.