Systematic reviews usually involve working with large numbers of references and you need to carefully keep track of the references you are working with. Reference management software packages can help with these tasks; they allow you to store, review and organise those references systematically.
When working on a systematic review, you are likely to use a PRISMA flow diagram to ensure you properly report your methods. Using a reference management package can help you to meet PRISMA requirements, by making it easier to track the number of references identified, duplicates identified, references screened, records included (or excluded), full text articles reviewed.