While JIRA is not a CMS or a system used to host a website or app, it is used to make these things happen.
I was lucky enough to lead a major agency into the adoption of JIRA and Confluence. Previously the project management team had been struggling to prove that we needed either more resources or better ways to pull information about where projects were upto.
Introducing JIRA and Confluence meant the team had a single source of truth. This allowed the teams to enter their time when working on a task, the PM team to make sure there was the appropriate tasks, and the Product Managers to ensure the backlog was in the right order.
Rationalising the systems meant the teams to concentrate on working together rather than context switching by using different systems.
While the company as a whole went through the change curve, when I was training the Liverpool and London teams on how to use it, they immediately saw the benefits and the adoption was pretty quick.