You have paper charts on board, covering the area you cruise.
And you have a GPS (well, most of you do). Often, that GPS is a chartplotter. So, those paper charts don't come out of the drawer too much, do they? You have them on board as a backup against the failure of the GPS, right? Are they current (probably not)? And have you checked the price of paper charts lately? Wow.
To get this straight right up front, I am not advocating abandoning the paper charts. They will work if the GPS dies, if you lose all electrical power on board, and even if the constellation of GPS satellites shuts down due to EMP.
Another (I am a belt & suspenders kind of guy) navigation backup is available to you if you have an iPhone (and perhaps other smart phones too, but I haven't checked). For less than the price of a single paper chart, you can have all the charts for a huge region in the palm of your hand. The Navionics app for the iPhone cost me $9.99, and that price included all the charts for the West Coast of the US, Alaska (including the north slope) and Hawaii.
These are excellent vector graphics charts, and include tides, currents, optional satellite overlays, and the ability to record tracks and store waypoints and routes. Everything is on the iPhone (except the satellite overlays), so once you have downloaded the app, no internet connection/cell phone coverage is needed for use.
Where else are you going to get a chartplotter for $10? And all the charts??
If you have an iPhone, you should have this one. It really is a no brainer.