It's an individual tool that security professionals use for their manual pen-testing. We use it for capturing the traffic, intercepting the traffic between the browser and the application. We try to manipulate the applications, the traffic so that whatever input that is accepted by the application is sanitized and validated. We try to analyze the application for input validation. All inputs are handled correctly.
Another use case is having a scanner module built-in where you can browse the entire application. The scanner can continuously scan the application for vulnerabilities based on OWASP Top 10 standards. Likewise, you can come to know what vulnerabilities are in the application. Later, you can go through the vulnerabilities one by one and triage them.
There are many different modules in Burp Suite. We have a comparator module where you can compare the request and response. You have the Repeater module where you can repeat the sequences. They can be used for other test use cases such as doing disciplinary attacks or brute force attacks on the applications.
Basically, there are a wide variety of use cases and applications.