Right now it's nearly impossible to pick up data when the API only sends back one result. Dual/Complex data-sources would pick up data based upon the results of another data-source. A real world example:
Campaign Monitor allows you to pick up a list of all campaigns, but if you want more information of all these campaigns you need to pick up each campaign individually.
A dual/complex data-source would pick up a list of all campaigns, allow you to select the campaign id by getting the list of all campaigns, and then pick up data for each of the individual campaigns as well. It would return this data as one data source, as opposed to multiple data sources.
- Data source 1: Get list of all campaigns
- Identify the ID field as a variable
- Data source 2: Loops through all the IDs returned from data source 1 to pick up all the results
- One combined result is created
Off the top of my head Shopify, Harvest, Basecamp, and Campaign Monitor would be just a few of the data sources which would benefit from this kind of data source.