Not necessary, AFAIK, unless you invoke vim using the alias "vi". If you call "vim" it'll start in nocompatibe mode by default. The nocompatible mode means add

Not necessary, AFAIK, unless you invoke vim using the alias "vi". If you call "vim" it'll start in nocompatibe mode by default. The nocompatible mode means adding some features to vim rendering it "incompatible" with the original vi. For example in the original vi you can only undo the last action, with compatible mode on vim will mimic this behavior.