The instructions in that file are terrible.
For example, it's very confusing to tell people, essentially, that
"you can make changes here, i.e., tpl_main_page.php. that will control whether page elements (such as sideboxes) appear on certain pages"
and then, at essentially the same time, say
"to make customizations to certain pages create a directory /templates/your_template_dir/pagename and put this file in there."
I read that, and I'm sitting there frozen, wondering if I should make my page-specific change by overriding tpl_main_page.php, as the instructions say I **can **do, **or **if I should make my page-specific change by doing the create-pagename-directory thing, which the instructions also say I **can **do.
Also, as kuroi mentioned, **where **down below should the code be dropped, for example, to disable certain page elements on certain pages. I'm left with dropping it somewhere and seeing if it works -- that's not a very good way of 'instructing' a user.
If I've misinterpreted something in this rant, then blame the crumby instructions for that page. My interepretation is based on them.