The use of strict meter, such as iambic pentameter, can become sing-song and seem amateurish, monotonous, for children, and other things you might not want your poetry considered. The occasional metrical inversion or substitution can keep things interesting. The caveat with this is too much pepper makes the reader sneeze. A little variation spices the poem, but too much makes it indigestible. You will lose the feel of the rhythm and meter if changing up is overdone.