By "breaks symlinks", he means that if you run `sed -i` (without `--follow-symlinks`) on a symlink, then it will turn the symlink in to a regular file. GNU sed

By "breaks symlinks", he means that if you run `sed -i` (without `--follow-symlinks`) on a symlink, then it will turn the symlink in to a regular file. GNU sed has `--follow-symlinks` which adjusts this behavior to edit the target of the symlink, and leave the symlink itself alone.