I like to consider the form a poem takes. When I talk about form, I mean more than pattern, which I think is the conventional approach to understanding form. For me, form is everything about the poem: patterns, yes, but also its shape, stanza formations, lineations, the way it appears on the page, etc. I approach form from a design standpoint: how does this element—the visual poem—impact the sound of the poem, the phrasing of the poem, the message of the poem...? I like to ask these questions of form because I think form is, like in film, so important to understanding the way poetry unfolds before us.
When writing poems, I experience form intutively. This is not to say I avoid thinking of form or that form is a mysterious, intangible element of the poem. No. The intuitive form means the form unfolds before me as I write, dictated both by content, emotional weight, speed of the text, and word choice. I find the strictest forms give license to writing the most emotionally-laden poems for me: there, form is a guardian, a containment, a safety net. I know within the form the my level of emotion about the subject will not overflow.
An example: when writing the Matthew Shepard section of my manuscript, I kept returning again and again to the ghazal. I have never loved the ghazal. But I pounced on it here, attracted to the soft and slant rhyming of the initial line and the percussive repetition of the repeated phrase. The first ghazal is called "I Watch You Be Killed with My Camera Eyes," and so, as you can imagine, it bears a lot of emotional weight, much witness. However, because something is being destroyed in this book, none of the ghazals take the visual look of a ghazal and instead the form—the pattern—is an undercurrent of the poem.
A later poem in the section, something I've called "Safe," was another intuitive form. Comprised mainly of couplets with very long (or very short) lineated phrases, I found when I was writing it I had to put four line breaks between the stanzas. It needed air. It needed S P A C E. But as I continued writing, even four line breaks was claustrophobic: I COULD NOT BREATHE in the poem. I widened the breaks to six. The poem itself plays with ideas of bars, of fence rails, of dividing the page up into smaller and smaller units. As a form, the poem is aware of space and its visual representation on the page. I think it's important for all poems to be this self-aware of their look.
I use prose paragraphs when the poem is urgent, when it is overwhelmed by itself. When there are no line breaks, the eye is free to follow text instead of drifting all the way across the page as it does (this is true; ask an ad copywriter).
There is pleasure in the form a poem takes. When a poem and its form are aligned, the poem breaks open, reveals more of itself than it would were it just broken into the way many contemporary poems read. I am suspicious of any poem in which the lines break at a fairly uniform place on the page—lines of equal length to me indicate that the poet may not have considered lineation in the writing or revising of the poem, or that they are working in metric or syllabic form. This is not to say I dismiss poems with lines of equal length: it is only a suspicion, and suspicion means only a cause for investigation.
There was one long poem I wrote, "The Fever Heart," in which the poem splayed itself all over the page. This was an intuitive impulse that occurred as I wrote it, but in the revision of it, I tamed many of those initial shifts. Many of them have remained in the poem, though, and that path the eye takes along the page is a significant, signifying element of the poem.
Poetic forms must be intuitive, must be internal to the poem, and they must be signifying elements of the work. It is true, then, that by this logic there must exist some poems in which the linebreaks do occur at a consistent point throughout the piece. But I think many poets today aren't thinking of form or lineation to the degree they should. I was fortunate enough to have a teacher who plagued me with concern for lineation. Although I was resistant then, the lessons have found me anyway, over time, and in ways that were meaningful to me.