Two-factor authentication requires a second proof of identity beyond a password, such as a code from an app, a hardware key or a push approval. It limits the damage from a reused or stolen password, which remains one of the most common ways a security system account is compromised.
A single password is one guess away from a breach when it is reused elsewhere. A second factor does not make the password strong; it makes the password insufficient on its own.
Factors that hold up
App-generated codes and hardware keys resist interception better than text messages. Whatever the method, enrollment and recovery need a documented path for a lost phone, or staff will share accounts to work around it.
Where to apply it first
Administrator accounts, remote access and any account that can export footage deserve it first. Service accounts used by integrations need their own controls, since they cannot approve a prompt.