Date-based campaign allows you to launch campaign on specific pre-determined date and time. Here you can specify the Time-zone that should be considered while launching the campaign.
Date-based campaigns are useful when you want to send weekly newsletters, event updates, etc. Your customers may be located in different country than yours. But you want them to receive emails when the time in that country is 10am. Date based campaign will allow you to do that by selecting the time and the Time-zone of that country.