When you purchase a GPS system, depending on the model and configuration settings out of the box, you will get a host of life changing utilities that will make your life easier and save you time and money everyday.
However, although the benefits out of the box are tremendous, the true value comes from repeated use and adding your own configurations, shortcuts, etc.
The more you customize the GPS unit to meet your needs, the more it "learns" about your preferences and requirements. You can add restaurants, stores, and anything you find during your travels that are not updated yet within the map systems.
Keep in mind that although not all data is one hundred percent accurate/updated all the time. That is always accurate enough to improve your driving and travelling efficiency. In other words, having something that is accurate 90-99 percent of the time is better than not having the tool at all.
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