No matter what GPS system you get now, you will always need to check to see if you are able to use that specific route. All the GPS systems are human programmed and just like any human, errors happen. We always check the route on our GPS once its showed us one, because even though it may figured the route it knows, you might know some inside secrets that might make your travels a lot easier and uncomplicated. GPS systems are good to help find particular addresses, but going from one city to another is sometimes better just looking at the map. We have a TomTom 3rd Edition and she (we call her Lola hehe) has us doing all kinds of weird things, like turning on roads thats not even there. She sometimes has us taking the long way around. This isn't because GPS system isn't working properly, its because there were some things programmed into the mapping wrong. Maybe because who programmed it made a mistake or they didn't have all the information needed to make it correct.
So, don't rely on the GPS all by itself. They are nice to have trying to find a particular street or address.