I was reading this page:
https://confluence.atlassian.com/jirakb/creating-issues-via-direct-html-links-159474.html
In our Chat-Ops projects, we send information from our monitoring tools to a chat-channel.
Based on the chat-information the user can - if desired - create a JIRA-ticket directly from a link offered in the chat message - with all the relevant information already filled in. The user can still modify all fields in the ticket before submission.
Using the REST-API instead is a different use-case. When you go that route the ticket will be created immediately - without any chance to enhance the ticket before the submission.
-- > It says on the page that Atlassian is taking away the feature to populate forms for creating new tickets. Is this decision really carved in stone? That would be a shame, as we use this a lot.