"The rain in Spain falls mainly on the plain."
Of course, competent versers would not write such doggerel in the first place. Instead, they would concentrate on softer rhythms: more substitutions (e.g. anapests, spondees, pyrrhics, double iambs instead of metronomic iambs), far fewer proximate/exact rhymes, and more variety in the stress levels.
Otto Jespersen's 4 levels of stress, "al-" is a three while the other three are fours, just as natural speech leaves "when" unstressed (i.e. 1 or 2).
Compare Shakespeare's lines to rap lyrics and the differences between soft and hard rhythms and between natural and metronomic speech become abundantly evident. Softer cadences, then, are associated with more sophisticated poetry while stronger beats identify more popular verse, including song lyrics. That's one view. Another is that if you want your words to be taken seriously by contemporary or future audiences they should be wrapped lightly, not tightly, in rhythm.