Although we bracket cats and dogs together as domestic pets, they are totally different from one another.
Dogs are pack animals and they need to convey their emotions to the rest of the pack. So when dogs live with us humans we become the members of their pack.
The easiest way for them to convey their emotions is by wagging their tails to show pleasure.
Cats, on the other hand, are loners and don’t feel the need to convey anything, unless they want food.
Cats use their tails as part of a complex system of movement and balance, especially when they are stalking their prey.