According to Pat Pattison, rhyme has a tonic function. Rhyme's job is to say, "I'm done." There are several rhyme types that say I'm done in different ways - similar to a cadence. "Perfect rhyme" and maybe "family rhyme" say "I'm done!" with much more certainty than less stable rhyme types such as assonance, consonance, additive and subtractive. Being aware of rhyme types can give you the power to choose your rhyme schemes consciously in order to support what you're really trying to say in your song. Interesting stuff!