Hi, welcome to the forum.
The Tablet S does feature a GPS module so mobile navigation is possible however I would not ditch your exisiting sat nav straight away if you rely on it.
Main reason why I say that is usually with the mobile devices/tablets/phones, the GPS module can in general be more twitchy to receive a signal so they tend to take longer to locate its position or use additional aids like wiifi to speed up the process.
The problem with being on the road are that free wifi spots in the UK are hard to find so if you find you losing signal, then you might have to park up and wait for a while. Another thing would be, you would need to find an application that downloads a map to your device rather than downloading parts as your drive as you would not have 3G/wifi access (depending on your locality or model).
Personally, I would not give up a sat nav just yet unless you do go for a 3G version which I would have to say the best recommendation if planning to use a navigation application.
Hope that gives you some insight.
