HashiCorp Vault is a secret management tool which provides a secure and reliable way to store secrets like passwords, access token, secret API key etc.
There are applications that need to interact with third party services and for that it needs various credentials. There are scenarios in which we need different credentials to process different requests. So, where will you store them? Can you really hard-code them and publish them to your sub-versioning tool? Ofcourse not. This is not a recommendable approach.