The button also helps with proper belt alignment. When the latch stays where it’s meant to be, the belt naturally sits correctly across the body. If the latch were free to move, the belt could twist or rest awkwardly. While the button isn’t a primary safety feature, it supports correct, consistent use. In most vehicles, it’s located just below the latch plate.
And some models include a second button to limit movement in both directions. If the button breaks or falls off, the seat belt will still work, but it may be less convenient. Replacement buttons are inexpensive and easy to install. What matters most is that the belt itself remains in good condition, free of fraying or damage.