If you’ve done much API generation then you’ll that you don’t want to have to make your users authenticate multiple times just because your API is going somewhere external. For example, if you have an API that reaches into Salesforce but your app uses Google SSO, you don’t want to have to present an oauth screen to your user after they’ve already authenticated. To work around this, you can use a JWT Bearer flow to login on behalf of a user and get a access token to work with.