-i is a "non-standard FreeBSD extension"<p>I have never understood the use for it. To save typing?<p>If we deny sed permission to write to any other file will it still work?<p>Could it be that there is an ephemeral temp file created? ed makes them, vi makes them. Is sed different?<p>What if the filesystem is a ramdisk? Does -i make any practical difference then? I always use a ramdisk as my filesystem.<p>I always found it easier to just avoid -i<p>This way I get portability.<p>The above applies only to BSD sed.<p>Not sure if GNU sed ever lacked the -i extension.
For convenience. And script clarity. If you have a move after standard sed, half of the commands in that group are for housekeeping. Sed -i makes the line more explicit.