What is the benefit of Monte Cristo’s disguises in this chapter?

The count is able to use his disguise to achieve a number of things in chapter 25.

This chapter witnesses the Count winning favor with the wives of both his archenemies. He plays with Danglars' desire for money, by buying his wife's horses from him, not because he actually desires the horses, but because he wishes to win Danglars' wife favor. He does this by returning the horses to her. This gesture also astounds and intimidates his enemy because the Count essentially throws away the huge sum of money for which he bought them. His ploy also widens the domestic schism that already exists in the Danglars' household, for husband and wife do not live in happy matrimony.

The Count also wins the trust of Madame Heloise de Villefort. By "saving" her from the wild horses, and rejuvenating her son, Madame de Villefort is so impressed with the miraculous Count. He knows the story will be related to her husband who will feel obliged to visit the Count. This is how the Count schemes to meet his nemesis.