why should you lock your domains or why do the registars lock them after a while?

can anybody tell me

Domain Name Lock is fast, easy to enable and keeps your valuable names secure. When you choose domain locking, your names put in the Registrar Lock, meaning they are secure not only on our site, but also at the registry, the very top level of domain administration. Domain Name Locking provides an additional layer of protection from inadvertent changes to your domain’s name servers, which could make them inaccessible.