Reasons to use frames:

• Consistent header or footer to your pages
  • No visible reload of constant page content
  • Limits the number of pages needing to be updated if all site-wide links exist only on frameset's sidebar page
• Includes variable and 'expandable' page content (scrolling)
• Convenient 'shopping cart' functionality (sidebar form)

Reasons not to use frames

• Bookmarks unavailable for all but the frameset
• When user adjusts browser window the changing frames within frameset sometimes revert to initial pages
• Search engine unfriendly
• User confusion
  • Printing
  • Navigation
    • Browser's forward and back button
    • If footer or side bar buttons are included on each secondary page linked to a frameset, no link to the frameset itself should be used (recursive frames).
    • If footer or side bar buttons are not included on each secondary page linked to a frameset then those who link to or print these Secondary pages will have no access to or information about the navigation scheme of the site. The pages do not 'stand on their own.'

Web Marketing Now quote

 More info: p.74 in Web Style Guide