There are several cases for making an HTTP request from a host application to another Atlassian application, for example:
Create a Confluence space when a Jira project is created
Automatically create Confluence pages for certain types of issues
Create release notes when a Jira version is released
Automatically decline apull requestwhen the associated Jira issue is closed asWon’t Fix
Typically these are done through calls to the REST API of the other application, or to ascript endpoint. However, you can also useremote controlto do the same thing.
Which approach you use depends on the specifics of the task in hand.