My complaint about most GPS devices is they do not take the routes I would think best.
More than once I have been routed through a city when a simple bypass would have been better. I know they have many options but I find them most useful once I am close to my destination.
To answer the OPs question, in all our travels I can say I have not yet had to turn around because of an unexpected clearance problem.
Admittedly I tend towards map and compass but I had many many miles accumulated before using my GPS, so I find it handy but not an absolute necessity.