This one is only used when the dataset flag is passed https://github.com/lucacopa/WMCore/blob/storeResults/src/python/WMCore/WorkQueue/DataLocationMapper.py#L135
Normally we would use the call by block:  https://github.com/lucacopa/WMCore/blob/storeResults/src/python/WMCore/Services/DBS/DBS3Reader.py#L503