The Wishon site is a good source of info, so is Pat Dempsey's
http://www.horsepowergolf.com which has a pretty clear article about why he spines clubs he assembles. He is a long drive champion, brother of the old Baltimore Oriole catcher, and an excellent club maker.
Only so called neutral spining is legal for clubs in USGA R&A sanctioned events. See the rules appendix or the USGA website.