Probably more than the regulators would have you believe, a bit like de-icing fluid has a negligible effect on aerodynamic performance . . . . . you know, "if we don't properly research it who can tell" because if we do. . . . Sheesh, a lot of flights are going nowhere in Winter.
Never underestimate the totally hypocritical /mercenary attitude of regulators when Boeing/Airbus/Govt power & $/€ are concerned.