Registrar lock protects your domain names from 'hijacking' : having your domain names stolen by being transferred out of your account without your permission. Enabling domain lock setting for all new registrations ensured that your domain names are protected from the moment you register them.
In order to modify the domain (for e.g.: if you wish to change your nameservers) you'll need to unlock the domain name. Also, third parties might be able to initiate a registrar transfer for your domain if it is unlocked, so we recommend turning locking off only when you need to make changes to your domain name servers or contact details.