Rhyme and reason - why things that rhyme are more true. Honest.

Language can have a powerful effect on people's perceptions.
When things rhyme people think the statement is more true. 
Of course if you ask anyone if it is true that things that rhyme is true they will laugh at you. 
All is revealed in a study named "Birds of a feather flock conjointly - rhyme as reason in aphorisms" 

We explored the role that poetic form can play in people's perceptions of the accuracy of aphorisms as descriptions of human behavior. Participants judged the ostensible accuracy of unfamiliar aphorisms presented in their textually surviving form or a semantically equivalent modified form. Extant rhyming aphorisms in their original form (e.g., "What sobriety conceals, alcohol reveals") were judged to be more accurate than modified versions that did not preserve rhyme ("What sobriety conceals, alcohol unmasks"). However, the perceived truth advantage of rhyming aphorisms over their modified forms was attenuated when people were cautioned to distinguish aphorisms' poetic qualities from their semantic content. Our results suggest that rhyme, like repetition, affords statements an enhancement in processing fluency that can be misattributed to heightened conviction about their truthfulness.

If you use rhyme in your advertising then likeability and the perception of truthfulness increases.
Remember OJ Simpson's trial? Well, you probably don't remember many of the details, aside from the media circus - details are far too complex to process. The jury - who had been subject to a barrage of facts and counter-facts over the course of a very long trial were told by Simpson's clever defence lawyers "If the glove doesn't fit - you have to acquit." And they did.

So, while advertising copywriters might sneer at the idea - maybe there is truth in the adage: If you've got nothing to say - sing it.