Changing Joomla 1.5 Backend Menu
The backend menu has various features which can be used by managers, administrator and super administrators. In general, a manager can access the backend and control website content for which he has permissions. Super administrators on the other end, can do much more. At times, issues can arise because manager priviledges are not enough while super administrators can allow a client to much control. If your hosting and permormance are issues, then so should be the makeup of the Joomla website. An example of a client having super administrator priviliges in a potential negative situation is one for which he can add extensions. Sure, in most cases this can be fine, while in other cases it could cause the installation of extensions which cause intense resource consumption. In a higher traffic situations, this site is a bad grape ruining performance for others.
To limit what can be done in the Joomla backend, such as installation of extensions and plugins, you need to hack core files to create a custom menu so that the user cannot add and change extensions. Read more here!