When you put cargo in an airplane, it needs to be tied down. Not so much so it doesn't fall over and break, but so that it doesn't move around and kill you, either by falling on you or by shifting the centre of gravity such that the airplane becomes unflyable. And kill you. Securing the load in an airplane is important.
When the load is people, the tiedowns are called seatbelts. Often the tiedowns are seatbelts when the load is not people, too, because seatbelts are easy to fasten, easy to adjust and certified for holding objects upwards of 200lbs in place. Humans don't usually have 90 degree edges on them, and objects don't usually have waists, so using seatbelts is discouraged for non-human objects. If your load consists entirely of non-human objects, then the seats and attached seatbelts can be removed from the equation (and airplane) entirely and dumped in the back of the hangar before the cargo is loaded and secured to tie-down rings.
A removable cargo tie-down ring consists of a square of metal with a ring attached to the top. It's about the size of a stack of seven saltine crackers, with a ritz cracker balanced edgewise on top. There's a channel in the bottom of the metal square so that it can slide onto the same rail that an aircraft seat attaches to, and a thumbscrew on the side to secure it in position once it has been slid to the desired location. Each tie-down ring, of course, costs over $200, about ten times more than a piece of metal with a ring and a thumbscrew on it ought to.
The law of tie-down rings is that there are never enough. One reason that there are never enough stems from the fact that there are often not enough, so captains learn to hoard them in their flight bags, exacerbating the shortage, and thus the hoarding. But even if you have a whole flight bag full of tie-down rings, you still can't secure your cargo properly because you can't put them in the right places.
You can only put the removable ones where there are seat rails. In other places you have to rely on the ones the manufacturer provided. You're lucky if there are any tie-down rings installed in the cargo compartment. I have worked with people who have resorted to the "pack it so tightly it can't shift" method. I suppose if you have literally packed the aircraft floor to ceiling with similar density cargo, and there is protection to prevent them from entering the cockpit, and you have forward emergency exits, you're covered, but just packing things in the rear cargo tightly enough that they are hard to remove won't cut it. Normal vibration or abnormal deceleration could still bring them down on top of you.
You have to plan the packing so you get the tie-down straps hooked into the tie-down rings before you bury them in cargo, and then just tighten everything down. The ratcheting cargo straps are nice, but I hate it when they get all jammed up in the reel.
Once I worked at a place that had truly awesome cargo nets that secured into custom recessed ports all around the inside of the cargo space. One airplane still had mismatched parts on the empennage from repairs following a years-ago towing accident, but the customers were safe from their cargo and the pilots could work efficiently. Rare that a company gets that priority right.