The baggage compartment in an airplane is like the trunk of your car (or the
boot, if you're English). When you want to move something, you open it up, push aside all the useless junk that has accumulated over time, and cram the suitcases, beach chairs, toys, and gifts in there as best you can. If you can close the door, it's loaded properly.
You may be able to get away with that in your car, but it's far from recommended procedure for airplanes. For one, an airplane baggage compartment has a maximum load limit, typically ranging from 100 to 200 pounds, depending on the airplane. The limit is based primarily on the strength of the aircraft structure. It doesn't mean the floor will buckle if you put 201 pounds in a baggage hold limited to 200 pounds. It does mean, however, that you increase the risk of overstressing the structure in extreme turbulence or under maximum certificated acceleration (G) loads.