If u want to use the same look up T/R more than one time,you should use compulsory Unconnected lookup.A common use for unconnected Lookup transformations is to update slowly changing dimension tables.I know these 2 uses.
Calling the same lookup multiple times in one mapping
Testing the results of a lookup in an expression
Filtering rows based on the lookup results
Marking rows for update based on the result of a lookup,
such as updating slowly changing dimension tables