We actually have 3 levels of "sound alerts" : All Sound on, Alerts only and Sound off.
Personnaly and as many road travelers, i prefer the Alerts only option.
But, when you are on a road for a long time (highway) and have a navigation change incoming, it could be very usefull to just have a little sound witch remind it to you.
It could be a good compromise between "All Sound on" and "Alerts only".