This is true. For a live, interactive performance to be smooth and professional, the speaker should feel very comfortable and natural with available content. At the same time, the process of remembering and navigating to potential content is easier than one might think, for two reasons:

Visual Clues in a Presentation Network act as constant reminders of available content, even if no actual presenter notes are used. Every time a switchboard is displayed, its links shout out reminders of where to go next.

The reusable nature of Presentation Networks means a speaker tends to use the same slides over and over again, in different situations and contexts. After awhile, familiarity with content happens naturally. Using main portions of the network often is as easy as simply talking.