Like blending in to protect themselves from predators...which I think someone already mentioned on here. Also I realized this point is strengthened because I remember reading in the Ellimist Chronicles, how the Andalites had an abundance of creatures that preyed on them back in their prehistoric past, so it makes sense that they'd need that camouflage along with 360 vision and a wickedly sharp and fast tail blade.
Though I think all those traits are kind evolutionary overkill if you ask me lol. Most prey animals on earth have one sometimes two strong attributes, but they seldom have THAT much firepower. After all, the ecosystems on the planet have to balance out, do they not?