After an unpleasant fuel related incident in a Gonad (N24) my then employer instigated a 'dip before and after flight' process as they investigated said incident.
On a trip from Tindal to Delamere to Darwin the dips showed that the Gonad burned signifficantly more fuel Tindal to Delamere than Delamere to Darwin. As best I can recall Tindal Delamere is about 1/3 the distance of Delamere to Darwin.
On another occasaion after dipping the tanks prior to refuelling, about 60+ litres of fuel went into the tanks over and above what the dip sticks indicated.
I am not saying they're useless, just that I remain ever wary of their accuracy.