John Dennison doesn't believe in them:
What is this talk of rules? A successful poem is not a matter of rule-keeping or breaking, but of faithfulness—trust in the possibilities of language and the various poetic traditions. Some forms have constraints, and I am very interested in the possibilities generated by working within and against these constraints. The question is not whether to use free-verse or strict forms, it’s about what’s needful, about the way each form sets up a micro-economy of agency and possibility within language. Free-verse, in an apparent paradox, foregrounds a kind of existential bind of constantly having to choose, having to assert control over language, to use it as a means of expression. In terza rima, on the other hand, one is constantly getting ahead of oneself (with the b-rhyme in the tercet) while glancing back from where you’ve been; it’s a promissory kind of form, constantly entrusting itself to unknown possibilities.