why does capote bother to relate the tale of the boy and johnny collecting cans?

This tale allows the reader to see how desperate the two were to not only blend in and hide, but how badly they needed money as well.

"The murders continue to haunt the town of Holcomb. Bobby Rupp and Susan Kidwell mourn the loss of their friend during the holiday season, and Bobby reminisces about happy Christmas days spent at the Clutter house. Dick and Perry continue to roam the countryside, one day meeting up with an old man and his grandson, who teach them to collect bottles on the roadside to exchange for refund deposits.