Great question! If you are looking to just store secrets you can just use infisical.

The real value of alter comes in when you want to give your agents access to end users credentials. When agents act on behalf of end user as a developer you have to manage multiple credentials and more importantly manage the mapping relationship between end user identity and the credentials.

Also, as agents take actions the problem of non deterministic actions become more pronounced. With alters policy guardrails any chance of actions taking negative actions is mitigated.

Lastly, the full compliance trails of what the agent has done ends up being quite valuble especially as agents take more autonomus actions!