Short Answer: Meat cleavers were traditionally hung on hooks, not only for safety reasons, but because it made the knives easily accessible to their users.
Other information: The hook ensures that the blade is under control when not in use and is an important safety feature of a meat cleaver. These knives are often kept extremely sharp and can prove to be a hazard in the work environment. The hook allows the knives to be stored away from the common area, and in a much safer location. These types of knives often don’t easily fit in kitchen drawers.
The holes are not intended to reduce the weight, or prevent the meat from sticking. It’s simply a utility function. Another simple use for the hole is that you can stick your finger in it to help pry the knife from meat if it becomes stuck. This is common when using a cleaver on frozen meat.
