If nothing else: It's certainly useful that mother's milk tastes good to babies. Imagine what an evolutionary disadvantage it would be if it tasted bitter.
To make it explicit for those who haven't tasted it, mother's milk tastes distinctly sweet (literally), in a way cow milk does not.
So yeah, there's a probable purpose for sweet receptors. An interesting question is whether seeking sweet foods in modern adult life, which would probably not have been available in our evolution, guides us to a healthy diet.
So yeah, there's a probable purpose for sweet receptors. An interesting question is whether seeking sweet foods in modern adult life, which would probably not have been available in our evolution, guides us to a healthy diet.