If I have coordinates for my destination my simple handheld GPS is quite useful. Having an arrow pointing "over there" as I miss my turn and have to loop back has been very helpful. On a business trip a colleague drove 30 minutes beyond the turnoff before he realized he'd missed it. (He was an hour late.)
That's a pretty basic use of GPS and is about all I seem to need. The biggest trick with it is getting coordinates for addresses. In one case I learned that a particular street had house numbers that followed the Japanese style of being in chronological order rather than logical order :-) GPS helped me find the street but the database didn't have the right house order. (I had to call & ask)
Routing, talking, suggesting routes by the GPS is unknown to me.