Automatic campaigns create lifecycle messages. Unlike a real-time campaign, an automatic campaign requires you to specify a combination of User Engagement State + Length of Time in Engagement State.
Sample Automatic Campaign Segment; Newbie + Day 1.
As you can see, Automatic Campaigns ask you to specify where the user is within your engagement lifecycle. Are they on their first day in the app? 7th day of inactivity? This enables you to structure a series of different campaigns depending on how the user interacts on that very first day.
Automatic campaigns are great for leading a user down the right engagement path and creating a rhythmic communication flow as you may be familiar with on email.