Answer:
In DWH loops may exist between the tables. If loops exist, then query generation will take more time, because more than one path is available. It creates ambiguity also. Loops can be avoided by creating aliases of the table or by context.
Example: 4 Tables - Customer, Product, Time, Cost forming a close loop. Create alias for the cost to avoid loop.
Example: 4 Tables - Customer, Product, Time, Cost forming a close loop. Create alias for the cost to avoid loop.