The smudging ritual comes from the Native Americans. They burn the herbs to make contact with the spiritual world. They do this, among other things, to dispel evil energies and to evoke good energies. Thus they cleaned the living spaces and even persons from bad energies. The ritual smudging has also found its way to Europe, although we usually do not evoke spirits with it. Here is mainly smudged to drive out unwanted smells and negativity. You can also smudge before or during meditation.
Sage is the most known herb to smudge with. This is because it has many positive effects. For example, it cleanses the air in the house, which also removes the negative energies. It helps relax and improves sleep. It takes away stress and boosts your mood. Its spiritual effect is to attract good spirits and bring positivity.