R is indispensible for anyone that uses and interprets data.
I analyze data straight out of tables provided in reports or articles as well as analyze usual datasets. The ability to quantitatively express, graphically explore, and describe epidemiologic data and processes enables one to work and strengthen one's epidemiologic intuition. In fact, I only use a very small fraction of the R package. For those who develop an interest or have a need, R also has many of the statistical modeling tools used by epidemiologists and statisticians including logistic and Poisson regression, loglinear models, and Cox proportional hazard models. The real advantage of R is the ability to easily manipulate, explore, and graph data.