1. As a template editor, I want to be able to check which comments use a certain template, so that I do not break them when I make updates the template.
2. As a template editor, I want to have easy access to the source code of any templates used by another user in a comment, so that I can help him/her to solve the problems they report about those templates. E. g.:
>Why am I getting this when I use the infobox? {{Infobox/foo}}
3. As a user who just noticed a page was converted to Flow, I want quick access to any pages transcluded into its header, so that I can update them to reflect the new system used in the page.
In normal wikitext discussions, if a user adds a link to [[https://en.wikipedia.org/wiki/Test1234|Test1234]] to a comment, then [[https://en.wikipedia.org/wiki/Special:WhatLinksHere/Test1234|Special:WhatLinksHere/Test1234]] will show that discussion page. This MediaWiki feature helps in the first use case.
Similarly, if the user inserts a template in his reply to some topic, then it will show up below the edit area, in the list of "Templates used in this page", with a link to easily get to the source code of that template. This feature helps in the second use case.