Power BI provides the Build permission as a complement to the existing permissions, Read and Reshare. All users who already had Read permission for datasets via app permissions, sharing, or workspace access at that time also got Build permission for those same datasets. They got Build permission automatically because Read permission already granted them the right to build new content on top of the dataset, by using Analyze in Excel or Export.
With this more granular Build permission, you can choose who can only view the content in the existing report or dashboard and who can create content connected to the underlying datasets.
If your dataset is being used by a report outside the dataset workspace, you can't delete that dataset. Instead, you see an error message.
Reference:
https://docs.microsoft.com/en-us/power-bi/connect-data/service-datasets-build-permissions