A freezer can handle more - if you have a large family or need to use the freezer to store food for a common space, then you need a large storage capacity. Freezers are ideal in this case because they can hold more food per square foot than any other type of freezer. This can save you a few grocery trips or not having to quickly use stored food to make room for new items.
Freezers hold temperatures more efficiently - Since the freezer door closes vertically, the weight of the door itself helps create a tighter seal than other types of freezers. Also, because cold air sinks instead of rising, and the hatch is on top of the unit, it's less likely to escape when you open the door to take out the contents of the freezer.
The freezer is more user friendly - the freezer is less likely to get frosted at the hatch entrance, allowing the user's hands and arms to comfortably reach for items stored inside. You also don't have to worry about accidentally opening the refrigerator. With a refrigerator, it's hard to do this without intentionally blocking or wedging it with another object.
Freezers are less likely to damage food - you want to buy a freezer because you want to preserve food and ingredients for a long time. With that in mind, you wouldn't expect your refrigerator to break them and disable their most important function. This can happen with any refrigerator that doesn't have an automatic defrost feature, causing the refrigerator to burn. However, the configuration of the refrigerated cabinet makes this less likely, as warm, moist air naturally passes through it when opened.