If you're using a hot bath to sweat, the process of heating the body helps to increase elimination of toxins. If you don't find yourself sweating in a hot bath, stay in there 30-45 minutes. It will accomplish the same results. If your body isn't used to sweating, it can be a process of re-activating that function in the tissues.
Some women, for example, may find that their ability to sweat is influenced by hormone levels, or lack of hormone regulation. That can change with ongoing sessions.