United failed to qualify for any type of European competition last season after finishing seventh in the league.
"I do think always that it is better to compete with the strongest clubs in the world that to train a lot of times in the week," Van Gaal told Sky Sports News.
"So I do think it is a benefit to compete in the Champions League because you have to compete with high-level opponents.
"All the teams has a lot of good players, not only 16 players but more than 25 players in their squad so you can play it that rhythm."
Van Gaal was speaking ahead of United's next fixture against Leicester City, who they play on Sunday.