Spam and Askimet modules - both needed?

I downloaded the SEO checklist module to help me determine how to set my new blog site for SEO. Anonymous users will be able to comment. It recommends both the Askimet module - which I already have, and the Spam module. Both seem to have the same functionality. Current anti spam measures I have taken include Captcha with the Math option, forcing the user to enter contact info, and require preview. The site is gong live this week, but I have no idea how much spam a Drupal blog site will get - Do I need both modules?