Remote interface is required when u know that ur ejb client and ejb object are residing on different computers. For example your web server and j2ee server are running on different machines.

Local interface is required when u know that ur ejb client and ejb object are residing on same computer/machine. This will reduce the overhead. Of course u can do away with remote interface but remote call always includes overhead when compared to local interface. local interface is just to decrease the overheads in case if you are sure that ejb client and ejb object are of same machine.