Cortical magnification has its advantages and its disadvantages. Predators benefit from cortical magnification because the high-detail vision in the fovea allows them to identify camouflaged prey or to keep it in sight while chasing it. For prey species, it is definitely a disadvantage, because they have the greatest need for sharp peripheral vision in order to identify predators. However, due to cortical magnification, peripheral vision isn’t too sharp, and they might not be able to detect a predator sneaking up on them if it is not in the center of their focus.
For the most part, however, cortical magnification is a good thing. It allows to closely analyze the things that we are focusing on, which can preventing us from harming ourselves, whether its eating a moldy strawberry or noticing the thorns on a bush that we were about to reach into. Our ability for high-detail vision has greatly enhanced consumer products, making them more appealing to look at because of their detailed beauty. Cortical magnification also helps us focus. If we didn’t have one area of high-acuity vision, and photoreceptors’ input was distributed evenly in the cortex, we would lose the ability to read, to avoid the deer standing in the middle of the road, and many more.
To be honest, if at some point in evolution we did not have cortical magnification, I believe that we would have developed it, because it is truly necessary for our survival. Now, we depend on our high-detail vision so much that about 25% of our cortex is devoted to the central 2.5 degress of our visual field (according to this study: http://psy.ucsd.edu/~sanstis/PDFs/Blurry.pdf) That number is mind-boggling to think about, and really demonstrates the importance of our high detail vision and cortical magnification.
