Automatically untangles and evens out the spacing between UV texture coordinates. You can choose to pin the border UVs so they remain in the same position while relaxing other UVs, or pin the selected or unselected UVs while relaxing any other UVs.
Use the following options to relax only selected portions of the UV shell.
Turn this option on to maintain the position of selected UVs. For example, if you want more texture space for an area on a face with very dense UVs, you could select these UVs, scale them up, pin them, then relax the rest of the UVs to eliminate any overlapping you may have introduced during the scale.