The purpose is call-to-action buttons is to visually guide the visitor into doing the main what you want him/her to do (the action).

By giving the visior multiple prominent call-to-actions, you're essensially destroying the effect of the CTA buttons, which is to guide the visitor into doing the one thing you want him to do. He won't know what you really want him to do and may not do anything at all since he's confused over what button he should click on. With too many call-to-action buttons they're essensially degraded to just being big buttons.