American here, in practice no. They are generally only the upper bound for dense neighborhood streets, throughout most other roadways you will be considered a poor driver if you go lower than the speed limit.
Considered a poor driver, and you can be ticketed for impeding traffic. I'd guess you are also more likely to undergo a field sobriety test if and when that time comes.
Where I live the major strode has a 45 mph speed limit and during most times of the day we only get to 35 mph but people make up for it by running the red light
The city of Tacoma, WA recently implemented new ALPR ticketing systems to enforce speed limits in northern Tacoma. They received so many hits, they had to build out a new system akin to a lottery for sending ticket / infraction notices.
To me, that seems like the city is entrapping its citizens to make up for a lack of revenue, when the data clearly shows the speed limit should probably be adjusted. But no, they move to develop a lottery system to send the infractions.