Functions provide an easy way of grouping commands that you need to execute repetitively. When a function is running, the positional parameters are changed to those of the function. When it stops, they are reset to those of the calling program. Functions are like mini-scripts, and just like a script, they generate exit or return codes.
While this was a short chapter, it contains important knowledge needed for achieving the ultimate state of laziness that is the typical goal of any system administrator.