You'd typically see this statement in two places: one, in the contructor of a class that implements a Remote service; or two, in the main() method of a class that starts a Remote service. Ex:
All this does is save the ServiceImpl class the hassle of extending UnicastRemoteObject, which has a constructor that does the same thing.
------------------
Michael Ernest, co-author of:
The Complete Java 2 Certification Study Guide