Kim Morrissey writes:
Punctuation is a way of establishing the pace that the poem should be read, and each punctuation mark in a poem signals a lesser or greater pause. [Richard comments: Of course, the reading aloud of a poem is an act of interpretation that can vary greatly, and the cues that punctuation establish can in some cases be ignored for remarkable effects.] [Leona comments: Some writers, like Kim, see punctuation as 'stage directions' for the performance of the poem, whether that performance is speaking the poem or hearing it in one's head. Others, like Richard see it as 'cues', that is, more a suggestion than an instruction. Still others, like me, see it as an aid to understanding (the grammar aspect) and as another element to be pulled out of the 'bag of tricks' that that makes up one's personal poetics. One of the effects I sometimes use is to leave out punctuation in a place it would be expected in normal grammar, which may produce a 'breathless' performance, but may also (for example) emphasise an ambiguity or suggest some aspect of the character of the poem's narrator, or persona, as Kim perfers to call it in her in her discussion here.]
The least pause is the space between two words with no punctuation marks. For instance, the space between the words: 'My ' and 'dearest' in the poem 'Dialectics'takes the least amount of time to say; when you add a punctuation mark, such as the dash at the end of the line, that punctuation invites the reader to pause longer, before going on to the next line.
My dearest–
The next smallest pause, after a simple space between words, is to use a comma, which invites the reader to take a breath, before reading on.
Then the semi-colon
the colon
the end stop (or period)
the exclamation mark.
There are other ways to signify pause, of course. One of the most common is to use extra spaces between words, so that the eye takes a longer time to read the next word. The 3-space spacing acts as a comma; the more spaces, the longer the pause. See Sudeep's poem, Offering, to see how various spacings affect a poem's pace.