You've seen it several times now: when you place 2 or more checkers on the same point, that point is blocked for your opponent. They can't land on it and they can't hit you.
This is the most important concept in backgammon: making a point. It's not just about safety — it's a strategic weapon.
A made point is a wall. The opponent must go around it. The more consecutive points you build, the harder it gets for them to pass.