After getting wet, dogs shake their fur to help dry it off. This is especially important for dogs with thick fur, as it can take a long time for their fur to dry naturally.
Dogs also shake their fur to release heat. This is especially common on hot days, when dogs need to cool down.
Dogs will also shake their fur to get rid of dirt or debris that has gotten stuck in their fur.
For example, a dog may shake its fur after being groomed as a way to show that it is happy with the grooming.
If a dog has fleas, it may shake its fur in an attempt to get rid of them.
In some cases, dogs may shake their fur as a way to assert dominance over other dogs. This is especially common in male dogs.
Dogs may also shake their fur when they are excited. This is often seen in dogs who are greeting their owners after a long absence.