The slam format is a competitive performance where a person performs an original poem, without props, costumes or musical accompaniment, in three minutes and ten seconds or less. Judges score the poem on a scale of 0.0 to 10.0 based half on content and half on performance. On the page, one can observe a poet's choices regarding line breaks, end rhyme, internal rhyme, punctuation, capitalization and other technical elements. In the slam the judges must assess the poem based strictly on what they hear. Because of this, the merits of a performance poem should be evaluated differently.
Performance poets guide the audience on a visceral level.
The performance poet has much more control over how the poem is experienced by an audience than the page poet does. This doesn't reflect on the quality of the poem, but on the variety of readers' approaches and audience perception. If I perform a poem for fifty people, the poem might resonate in those people differently, one relating to an experience expressed, another is particularly attracted to a turn of phrase. But all fifty of those people have heard the same presentation of the poem. A poem on the page may be translated by a particular reader in one tone, and take on a different mood if read by a different reader.