You can take backpacks and throw them through closed door and walls.

This can be a problem for base defense since a player can pull the pin on a grenade and put it back in the bag quickly and throw it through your closed doors and gates.

It also is just a problem for people who use are using a exploit to spawn in your base. They load up your gear into a backpack and throw it through the wall or gate to a buddy all without destroying anything.