If you know when a certain occupation occured in an area of interest, it is useful to track people from that time period by looking closely at tin cans which leave important clues about dates. A big part of gold prospecting is historic research and this technique is one of many which allows a prospector to associate finds in the fields to the research they do at home. Relic hunters or amateur archaeologists may also find it useful to have a basic understanding of the dates in which many common cans were first introduced.