The phrase "important function" refers to a task or role that plays a significant and necessary role in a specific context or situation. Full definition
The most important function of such connections, they say, is empathy and shared experience. (sciencemag.org)
Insulin has a number of important functions in the body, including storing glucose in liver and muscles and stimulating muscle protein synthesis. (ketodietapp.com)
Pharmacy technicians perform some of the most important functions in a pharmacy setting. (medicalassistantschools.com)