Reading online is slower and quickly causes eyestrain. Online readers are impatient. They want to be able to find what they need quickly. Online readers aren't linear. They move quickly through the document in whatever order suits them as they try to grab the information they need.
Online readers are skeptical.
They want online writing to assert its credibility right away. They hate marketing hype. Readers hate to scroll. These aids include menus, tables of contents, and short summaries of what can be found on other pages. Highlighting key words, providing meaningful heads and subheads, and incorporating clear links.