The UV Pin node is used to track positions on a deforming surface, similar to the Proximity Pinnode. As the name suggests, UV Pin derives locations from UV coordinates, so you can specify exact coordinate locations for your pins.
See Create a UV Pin for steps on how to add a UV Pin to your geometry.
UV Pin is good to use when you have clean UVs; it does not work well with duplicate or questionable UVs. The
UV Pin node lets you scrub the UV values in the Attribute Editor to move the
UV Pin across the surface of your object.
A UV Pin added to NURBs geometry
The UV Pin node is good to use when precise positioning is important, for example if you were aligning a feature in a displacement map where you needed to know the exact position of the UV, or if you were animating across a surface.