new fish graphs

Im looking to get a new boat and want to set up right. why are lots of people putting 2 graphs on con. and bow? How do they use each to do what?Would like to know before ordering new rig. Is one better than other at ease of use?Thinking of Humm. onix .

bump

2 graphs just gives more screen space. Like dual computer monitors. Controls work on each unit. Side scan on one and chart/sonar on the other.

Personal preference is Lowrance.