The screen shots below show that even while I am not importing the catalogue, I can still import one of the building blocks (i.e. the row) associated with it.
Catalogue Not Seleted
Row Definition Selected
This is a great convenience for heavy report designers who like to make a full backup of their building blocks by exporting them prior to an all day (or more likely all night) report design session!
It is also a great feature for consultants to make use of when creating a reporting package solution or to troubleshoot report design.
Sleep well!