Maybe - it depends on the application. If something just needs to be "tight enough to hold together but not to strip the bolts" then 16-24 may be perfectly fine. In that case we would refer to 20 foot-pounds as the nominal value, but the actual torque can be within 20% of that and still work for that use case. I might even be able to just use the torque setting on my cordless drill and that will be good enough. Other applications obviously require greater precision, along with a more accurate and precisely calibrated torque wrench.

About 20% is the most commonly seen figure. My wheel guy gets it a lot closer than that, and even gives me a printout, probably generated from the Park Tool app.