I have both, a stand-alone unit and GoogleMaps on my phone. I've switched over 100% to GM - the stand-alone unit is on the floor of the car and hasn't been plugged in in 4 months.

I use it routinely, even if I know the trip. In fact I'll fire it up tonight when I leave this restaurant for the trip back to the apartment, because I have been known to get so into driving that I miss my exit. And because I'm emotionally scarred by 5 years of living in NJ back 30 years ago (when the sign at the bottom of the ramp reads "I know you just got OFF the highway sucka, but you ain't getting BACK ON within 15 miles").