We all know that thousands of emails are compromised every day. Their passwords are hacked.
This can happen when a large website is hacked. Most websites ask for customer email ids and personal details like name, location, etc.
When the customer database of such a website is hacked, our email id, name, location, Date of birth, and some other details fall in the hands of hackers.
Haveibeenpwned.com is a website that monitors these breaches (leaks) every day and helps us check if our email id was recently compromised.
They also have a service where you can be notified if your email is ever compromised (hacked or stolen as part of a breach). There is no charge for this service or for checking if your email has been compromised.
In spite of rules that require companies to share when their database is hacked, many customers never hear about these hacks. So, a service like haveibeenpwned helps individual email users a lot.