f you analyze the Billboard Hot 100 at the end of every year from 1960 to 2013, and look for what words the artists attempted to rhyme together (and only take one example per song, to avoid repetitive choruses), it seems the most popular rhyme pair in modern pop music history is “do” and “you.” 

Rhyme aids in memorization.(There is a reason that you cannot GET that song OUTTA YOUR HEAD)

and possible mesmer-ation

 Long before there was even paper

 to write upon

 people recited their entire tribes' histories to each other IN rhyme

Rhyming made this easier. 

Rhyming also aids in conveying rhythmic properties

an  emphasis can be placed on the rhyming words in time to a beat, as in most music in the western world...

In psychology and psychiatry, clanging refers to a mode of speech characterized by association of words based upon sound rather than concepts. For example, this may include compulsive rhyming or alliteration without apparent logical connection between words. This is associated with the irregular thinking apparent in psychotic mental illnesses (e.g. schizophrenia).

Clanging refers specifically to behavior that is situationally inappropriate. While a poet rhyming is not evidence of mental illness, disorganized speech that impedes the patient's ability to communicate is a disorder in itself, often seen in schizophrenia.