The variance-covariance approach, also known as the parametric approach, simplifies calculations by assuming that returns are normally distributed and by using the covariance matrix of asset returns to estimate portfolio risk. This approach provides significant computational advantages because it reduces the complexity involved in risk calculations. On the other hand, the full revaluation method (often used in Monte Carlo simulations) involves revaluing the entire portfolio under various simulated scenarios, which is computationally intensive. Thus, option A correctly identifies a key methodological difference.