By default, the X server automatically loads the following modules from the /usr/lib/xorg/modules/ directory:

The default directory for loading these modules can be changed by specifying a different directory with the optional ModulePath parameter in the Files section. Refer to Section 30.3.1.4, “Files” for more information on this section.

Adding a Module section to /etc/X11/xorg.conf instructs the X server to load the modules listed in this section instead of the default modules.

For example, the following typical Module section:

Section "Module" Load "fbdevhw" EndSection

instructs the X server to load the fbdevhw instead of the default modules.

As such, if you add a Module section to /etc/X11/xorg.conf, you will need to specify any default modules you want to load as well as any extra modules.