This is a feature that existed in AX2012. It's to budle the imports. If a single line failed whilst importing a file, the system fails the whole file from being imported rather than allowing the successful files lines in an import file from being imported.

For example, when importing Journal Lines file into D365 using the Data Management framework, that whole file will be dealt with as one transaction. So, if a line failed whilst imporitng the whole import file should be aborted.