It is helpful for bug tracking in software development. If developers are doing some work and testers notice some defects, they can flag it in JIRA. For example, I track my day-to-day work in JIRA so that others know what I'm working on. They can look at JIRA and don't need to contact me. From JIRA, they can find out that I am working on this project and spent two days on it, etc. It's used for so many things, like task management, bug tracking, and release management.
JIRA is not for deployment. For deployment, you are going to use some tools like Jenkins. It's meant for all the features that are going into that deployment.
Different teams within the company use JIRA. For example, everybody in the engineering section uses it, so altogether, that's around 200 people.