SSL/TLS certificates enable encryption of the data sent between your browser and the website you are visiting, preventing attackers from intercepting or modifying information. They also verify the identity of the website owner.
Why check a certificate?
Network administrators and developers frequently need to check certificate validity to ensure their domains are actively secured, verify that an auto-renewal system (like Let's Encrypt) successfully deployed a new certificate, or to audit the Subject Alternative Names to discover other subdomains bound to the same certificate.