“Shooting Ranges Are Almost Always Flat. Real Life Isn’t.”, as explained by renowned firearms expert Ryan Cleckner.

Gathering data for your rifle at certain distances is useful, but it’s only reliable when shooting at targets of the same angle (above and below your position and side-to-side lean of your rifle). If you have a change in angle, and the target is far enough away, you might just miss if you don’t compensate for it. This article on RecoilWeb will help you understand how.