The real fun comes when you want to run commands in every shell, whether interactive or not. For example, aliases that you want available when you use shell esc

The real fun comes when you want to run commands in every shell, whether interactive or not. For example, aliases that you want available when you use shell escapes like ! in vi. The only way to do that is to have the file's path explicitly in $ENV, or $BASH_ENV of course...