It is very essential to lock the domain after it has been registered so that there is no unauthorized access to the domain. The information registered with the domain can be changed and the domain can be transferred if the domain name is not locked which is certainly not in favor of the domain owner :(
Domains are locked by an EPP code which is also known as Authorization code of the domain. EPP code of the domain is generated by the Domain name registrar once the domain is registered. Hence, the Domain name is automatically locked
