A CAA record names the certificate authorities allowed to issue for your domain. Without one, any publicly trusted authority may issue a certificate for you, which is the default state for most domains.
What it protects against
Mis-issuance. If somebody convinces a certificate authority to issue for your domain — through a compromised validation path or an administrative error — a CAA record naming only your actual authority means most authorities will refuse before it gets that far.
Is it worth adding
It is a single DNS record and it costs nothing, so yes. It is not urgent for most businesses, and its absence is not a fault. It is one of those gaps that is worth closing while you are already in the DNS panel.
The catch to know about
If you add a CAA record naming one authority and later switch providers, issuance fails until you update it. That is the intended behaviour, and it is why a forgotten CAA record occasionally causes a confusing certificate failure years later.
This is the short version. The full guide covers it properly: read more.