Vi (and ed) are the only text editors required to be included in the POSIX spec. A base Unix (and most Linux) installs will have some version of vi or vim installed by default.
If I'm working on someone else's box this pretty much guarantees I can edit files with my basic vi knowledge without having to install a different editor.
If I'm working on someone else's box this pretty much guarantees I can edit files with my basic vi knowledge without having to install a different editor.