Layouts determine the type of flow for your event. Will there be group interaction amongst peers? Crescent Rounds may be a good choice for group interaction with everyone facing forward. Is it a listen and learn training? Classroom seating may be a better choice because everyone would be facing forward and have a table in front of them to take notes.
Also, take in account if food and beverages will be served and if the seating is compatible. There are several layout options with the most common seating arrangements including theatre seating, banquet rounds, classroom, conference, and u-shape. On your next event, visualize the agenda to determine your best layout.