Hi, thanks for reaching out. I've worked on a similar inquiry and the advise is to not delete data stored in default datastore to avoid weird errors. The option to easily delete experiment runs is on the roadmap. Here's a similar thread. Feel free to raise and track feature request on ideas portal.
According to documentation, when you create a workspace, an Azure blob container and an Azure file share are automatically registered as datastores to the workspace. They're named workspaceblobstore and workspacefilestore, respectively. The workspaceblobstore is used to store workspace artifacts and your machine learning experiment logs. It's also set as the default datastore and can't be deleted from the workspace. The workspacefilestore is used to store notebooks and R scripts authorized via compute instance.