I needed to enable smarty templating for plugin_categories.tpl. The reason is that my website is going to be serendipity embedded, and it's going to have a large space at the top for introductions and other website related things, and I wanted the serendipity category links to anchor past that. For example....:
That worked, but I'm told that enabling smarty templating for the category plugins impacts performance. How bad is that performance hit? and is there a more efficent way of doing what I'm trying to do?
We're still discussing exactly how bad that hit is. We know there MUST be some hit, but we don't know how much it is. And since Serendipity is billed as "built for speed" (among other things), we avoid the templating for frequently-used stuff. Carl's found at least one site that says Smarty templating is fast enough for high-volume websites.
My opinion is: if it ain't broke, don't fix it. You say it's working n your website, so I'd say leave it be.
If you want to make the changes directly in the PHP, you can do that, too, in plugins_internal.inc.php. You'll lose your change on the next upgrade where that file changes, though. Speed has risks.