In addition to its role in cycling the action of a weapon, the BFA also prevents debris from the blank round (and in some cases, inadvertently loaded live rounds) escaping. This debris could cause injury to nearby personnel if the BFA has not been fitted or has fallen off.
The BFA contributes to more than just weapon operation by preventing debris from blank rounds and, in some cases, live rounds from escaping. If the BFA is missing or detached, this debris might cause harm to individuals near it.