Used for a number of different things such as space clearing, connecting to higher beings, opening and closing of cermonys and rituals as well as other forms of spiritual or prayer work.
Every so often it is also good to cleanse your altar bells and this can be quite simple. One cleansing technique is to light a sage smudge stick and have the smoke go over the altar bell for several moments, while other people prefer to cleanse for 20secs or so placed into a bucket of sea salt and water. Because most alter bells are brass or silver plated dipping them into a sea salt bath will cleanse your bells fairly well. Both methods work great.