I first started using Jira when I was working for a very big telecom company in Gurgaon (now Gurugram). I was asked to setup and manage Jira instance. My responsibility was not only limited to customising the tool but also to make sure new teams can be migrated to it. That time the teams were using Jira to keep track of their test campaigns and test cases. This was obviously easy in Jira, just create parent and sub tasks along with relevant workflows. I remember I used to import data using CSV which was a life saver.