Lighting bhimsen camphor before God symbolizes that if we burn our illusion or ego with the fire of true knowledge, we shall merge with the God, leaving no residue.
Bhimseni camphor is used in ayurvedic medicine since ancient time. Camphor is most often used for spiritual cleansing and protection the classic usage is to spiritually cleanse a room
Camphor is burnt to perform Aarti (circular movement or display of the lamp in reverence before the deity or the idol) before the deity. Just as God rotates the sun and the moon around you, you imitate the same and thus offer and move the camphor lamp before God to bring joy to you.