From an interview with Andrew Kozma at 32 Poems blog:
2. Do you see spoken word, performance, or written poetry as more powerful or powerful in different ways and why?
I seem them as powerful in different ways. Spoken word and performance poetry have more to do with the skill of the writer as a performer than they do with the power of the poetry itself. A brilliant performer can bring you to tears with your tax return. Because of this, it’s hard to tell from a performance whether the poetry stands on its own as poetry because the voice of the performer gets in the way. In addition, spoken word is crowd-oriented, meaning that your reaction is somewhat determined by the reactions of those around you. It’s a communal experience.
Written poetry, on the other hand, is intensely private. Even if you like the same poets and love the same books as another person, chances are that you are receiving different things from the poems, and that those things are different than what the writer intended. Text is like e-mail in this: the skill of the writer narrows the field of what the reader interprets, but it is still an interpretation.