I noticed in this skull strip tutorialhttp://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/SkullStripFix that sometimes when adjusting the watershed threshold the -no-wsgcaatlas option is used. I understand that it means that the atlas, which is used to assist in detecting physical features while stripping the skull, is not used during this step. Why wouldn't you want to use it?
-- Vincent