In the real world, new diseases emerge from complex environments. To learn more about how, scientists set up whole artificial ecosystems in the lab, instead of focusing on just one factor at a time.
Epidemiologists want to quickly identify any emerging disease's potential to spread far and wide. Dependent on a number of factors, this R0 number helps them figure that out and plan accordingly.
The novel coronavirus spreading outward from Wuhan, China, will get an assist from a subset of infected people who transmit it to many others.