Keeping a changelog and tagging the releases serve various purposes
It's easy to identify the differences between versions (e.g. Production vs Staging) so everyone is aware of what is running at a server just looking at the CHANGELOG.md
Helping the Product Team
Sometimes the product team may not be fully aware of what are we deploying or what the differences are between what is deployed vs what we are testing. The CHANGELOG.md will be easier to understand than checking commit messages. Commit messages are much more technical oriented and written for developers instead of customers/managers.