Who here has ever said "gee I sure love getting spam comments on my website/site blog"?
Right. No one has ever said that. Spam is super annoying, and while Akismet is pretty good at blocking spam comments from being approved G.A.S.P is a great second line of defense against spammers and spambots. It's easy to install and it's easy to use. Making people read a captcha phrase or solve a math quiz can be annoying (especially when the captcha phrase is hard to decipher, like is that a g or is that a q sometimes you just don't know).
G.A.S.P is simple plugin for people to use. They just have to check a box. No fuss. It works. End story.