Employees prefer to ask how to do something rather than read instructions. Seeing a play performed is a larger experience than reading the script. Additionally, speakers connect with their audiences via eye contact and physical bearing. This connection is a integral part of spoken communication, providing speakers with immediate feedback to make course corrections or respond to audience queries on the spot. When a speaker connects with an audience both speaker and audience get a jolt of energy.
Writing has a different set of strengths and is often epitomized as the language of information.
It is permanent, detailed, precise and structured for re-use and understanding. Writing transcends time and space. Contracts, wills, legislative and other legal documents are in writing because of these attributes. The speaker creates, memorizes and delivers the speech in the argot of writing rather than in the idiom of speech. Delivery is formal and impersonal rather than interactive and personal.