To prepare for the cross-country meet, a skier decides to significantly increase the amount of carbohydrates in his diet (a technique also known as carbohydrate loading). Why might this be beneficial to the cross-country skier

It is beneficial to the skier in that more carbohydrates will give rise to excess glucose thus the energy required to ski.

Explanation:

Eating food that contains higher amount of carbohydrates will cause the muscles to store excess glucose in the form of glycogen and this can be used for the energy in short bouts required for skiing.

Furthermore, it is useful in providing energy over long course of time. I

But in the question context, the skier needs rapid energy source and this energy is provided by muscle glycogen.