What is PhantomJs used for

What is PhantomJs used for ?

When I wanted to run my automation scripts on CI/CD pipeline back in 2017, I was experimenting the headless browsers starting with PhantomJs.
Now Phantomjs is a discontinuoed headless browsers due to poor maintenance and support. 
Selenium automation utilized PhantomJs when it needs a non GUI mode executions on jenkins server when there is no browser installed on it or no support from docker containers.