Do I need to map sessions that should be visible to everyone in my event?

No, you would not need to map sessions that should be visible to everyone in your event. All unmapped sessions are visible to all attendees.

P.S. In case this didn't fully answer your question or want to see a live demo or ask live Q&A, join our Event Overview Whova Academy! We host a live session covering the Whova Overview and Setup every Monday at either 9AM or 1PM PDT.