Should I use a template engine?

I have my own mini-template thing like this:

function template($content) {


 global $title;
 global $main;
 global $menu;
 global $userinfo;
   $filename = "./themes/theme.html";
   if(!$fd = fopen($filename, "r")) {
                $error = 1;
        }
   else {
      $template = fread ($fd, filesize ($filename));
      fclose ($fd);
      $template = stripslashes($template);
      $template = eregi_replace("<% title %>", "$title", $template);
      $template = eregi_replace("<% main %>", "$main", $template);
      $template = eregi_replace("<% content %>", "$content", $template);
	  $template = eregi_replace("<% menu %>", "$menu", $template);
	  $template = eregi_replace("<% userinfo %>", "$userinfo", $template);
      echo "$template";
	 
    } }

function home() {

global $title;
global $main;
global $menu;
global $userinfo;

Code (markup):

Would that be good enough for a decently large php site or would it be better to use a template engine. Which I have no clue how to use (Ex. Smarty)

 

if your project big enough try it. it to big for small projects

 

If your site is complex with a lot of pages and has a lot of traffic and stress on the server then I would go with something like Smarty because it has built in caching. If not then your template engine you made would work perfect.