Do you  need...

Some people like to be able to overlay their chart onto Google Earth, or vice versa, and there are chartplotters, such as Fugawi Marine ENC, that will do that.  This feature may be quite useful when going into a poorly surveyed harbor. There are sailors who feel it helps them get an overall sense of a new destination.

There are chartplotters that will combine surface navigational charts with either Google Earth or land topographic maps, and create a three-dimensional view of the land and sea. This is most useful with poorly charted harbors.

It may be useful to have street maps available, to know where to go when you get off the boat in a new port.  Products that support these include Fugawi Marine ENC. If you opt for this feature, you may want a printer on board so you can take directions with you.