The definition of event segments has an effect on scheduling ad breaks manually: Via this options tab you may define the number of breaks and the segment positions for the respective event segments. On scheduling an ad break manually (number and position) the segments are set according to your definition. You may define as many event segments as necessary.
The definition of event segments only plays a role on the manual scheduling of ad breaks into events. Please consider that on using an ad break model these default settings here will be overwritten, i. e. they will NOT be applied for your plan. The same is true for events with asset information: if the asset of a scheduled event carries segment information, then these settings are paramount.