There are two types of Automated Campaigns: -
1 - Date Based Campaigns
2 - Linear Campaigns
The Date Based Campaigns are a great way to manage events and other campaigns where there is a key/target date which you want to hang the campaign around. This means that you can create actions/steps to go before the event as well as after the event!
This also means that if you have actions which go 30 days before the event and you add someone into the event 10 days before, the system will not send them anything that has passed either, they will only get what happens next
and don't forget that you can use our date/time custom field to fine tune your outbound communications too. For example you can create a "Next appointment" date/time and in addition to communications before the date, you can also send a communication on the day itself at a specific time e.g. a SMS 2 hours before an appointment.