I always wondered why smudging cleared a space of heavier energies. I came across a few different pieces, but this made the most sense to me. Smoke from herbs like sage have the potential of seizing the positive ion in the air molecule and extracting it. The positive ion is the electric charge in air that can be harmful to you.
"Shamanism is the foundation of Space Clearing and Feng Shui and both are very magical art forms. The sensing of subtle energies, ghosts, thought forms all take time and continual practice to become skilled at discerning what is real and what is not. Shamanic truths and techniques have been used by every culture from the prehistoric through the great classic civilizations and on through the present."
"Smudging with smudge sticks is one of the best ways to remove negativity, negative forces, and unwanted energies from your home. There are many different ways you can perform a smudging ritual or ceremony on your home that is quick, safe, and effective, however this post will go into just one general ritual that basically anyone can do and use as long as they have the proper smudging materials needed to perform it."