How often have you searched for a process, using ps and grep?
$ ps -ef |grep emacs peter 7107 1 1 09:10 ? 00:00:08 /usr/bin/emacs-snapshot-gtk peter 7377 7050 0 09:19 pts/0 00:00:00 grep emacs
It always reports one more process than you want to see … namely the grep process itself.
In the example above, the process 7377 is the grep process itself. What you really want is the 7107 emacs process.
While this is really harmless (albeit annoying), it can be a real pain if you put this in a script. In that case, you have to parse out the grep process itself.
You can trick grep not to report itself by enclosing a character in the search string in square brackets:
$ ps -ef |grep emac[s] peter 7107 1 1 09:10 ? 00:00:10 /usr/bin/emacs-snapshot-gtk
Square brackets in bash are character matching patterns. emac[s] will only match the string emacs.