The coil is used for target practice by Warehouse agents, as any Tesla blast fired near the Coil is automatically drawn towards it, no matter how far off their shot is. When the Coil is activated an electric current runs through it, so anyone that touches it will be shocked. Also, a large ball of electricity seems to float above when it's active.
In "Love Sick", Pete, Myka, and Steve were using the Coil for target practice.
In "Parks and Rehabilitation", Artie ran the electric current generated by the Coil through Hans von Bulow's Piano Wire and wrapped the wire around an arrow. Myka then shot that arrow into Leonardo da Vinci's Gargoyle and the electric shock brought down the artifact.