The modern-day practice of burning sage (or sage combined with other dried herbs) in personal smudging rituals and ceremonies is based on a combination of the spiritual, medicinal, herbal and cultural teachings of the past.
Essentially, a smudge ritual or a smudge ceremony is performed to correct the energy in a home, in an office, in an object, or even in a person. This is accomplished by burning sage or sage and a combination of herbs, in a focused, intentional way to cleanse out negative energy and to replenish positive, healing energy.
Some ideal (or necessary) times to smudge/cleanse your space would be:
When you move into a new living space
When you begin a new job or start your own business
Before and after a guest enters your home
Before and after a yoga or healing session
After an argument or any illness
Upon returning home from crowded situations