Deployment Pipelines and Azure Devops

I'll elaborate on jeffshieldsdev answer-

Since May, Power BI deployment pipelines have REST API that can be triggered from ADO pipelines and promote content through the stages in a Power BI pipeline. These APIs basically do the same operation that you can do through the UI of Power BI Service, but with all the value that ADO provides- scheduling dpeloyments, cascading multiple deployments, approvals, tests and many more.

What your colleagues asked about (i think) is why even use Power BI pipelines, when you can just use ADO pipelines and trigger regular Power BI REST APIs. 

Well, there are quite a few advantages. to name some:

1. Power BI pipelines allows for a holistic deployment of almost all the content in Power BI together, while REST API mostly support single artifacts that aren't related.
2. In pipelines we also maintain the original connections between artifacts, as it was in the source stage. no need for 'rebind APIs'.
3. Rules- PBI pipeline rules allow you to maintain connection and data to the target source, while with regular APIs you will need to set it after the import and refresh again, which causes downtime.
4. Easier way to publish reports and datasets separately, even if you didn't separate them in the PBIX files.
5. We are working now for APIs that will enable devs to build PBI pipelines from scratch, so that everything can be automated from scratch.

If you are using the same data source connection when working in Dev/ Test/ Prod, then there's no problem using 'Import API'. But if you want to switch connection between environments, as many customers do, this is where rules have the advantage vs. using the regular 'Import API'.