DRY for WordPress Templates
When displaying posts in your WordPress theme, you usually have the same chunk of code in multiple places throughout your theme, and it usually never changes.
For example, you typically have the same code in index.php, archive.php, search.php etc. and even the single.php page contains very similar code.
That doesn’t make any sense at all. A better approach is to include that code in one file, and reference it from there: Don’t Repeat Yourself.