User-created functions and scripts often make the life of an R user easier. If a repetitive task involves several different lines of code, creating a function or script to do the task saves time. In S4, methods for generic functions are the functional side of S4 and require special treatment.
Designing plots is one example of when a user-created function or script makes sense. Plots often take several lines of code, and the design of a plot is usually an interactive process. From command line R, creating a function to do the plot and making changes to ...
