Under the ground surface there are millions of miles of utility lines running. Calling 811 to have these areas marked out is extremely important before starting your project. Otherwise you run the risk damage to your property, utility service outages to the entire neighborhood and potential fines and repair costs.
After the locators mark out the utility lines, make sure to dig around and not on the lines. Some utility lines are buried at a shallow depth and it only takes one hard shovel thrust to potentially break the line and bring some big trouble. So before you start your next project that requires digging--make sure to give 811 a call!