What is the purpose of and significance of a demarcation point?

Actually,The demarcation point is also referred to as a Network terminating interface or demarc

• The demarcation point defines where the telephone company’s responsibility for maintenance ends and the consumer's responsibility begins. 
• The demarcation point contains a surge suppressor to protect the wiring and connected equipment in a customer's home from external or internal damage.
• It is also permits consumers to disconnect from the telephone company's wiring for troubleshooting.