The most obvious reason for saving bandwidth is that it is very scarce. If your application takes up large amount of precious bandwidth, then it cannot be utilised by the customers not having high-speed connections. In the abouve technique, mobile hosts are made to to cluster together and leads to the use of fewer cells to save the scarce wireless bandwidth. wireline bandwidth is saved by making the the paths in the multicast tree connecting to the selected cells share more common links.
The whitepaper of this topic is available in this link;
http://whitepapers.techrepublic.comabstract.aspx?docid=1203933