Before you start to modify a Joomla 3.x template's CSS styles, you need to consider which method is the optimal solution for your project.
The most important is fact that we release Joomla 3.x template updates quite frequently, so you should take into account that you may need to update your template files in the future.
Sometimes the standard way of assigning modules to the menu may be not a sufficient solution for your website, particularly if you would like to make any module contingent upon any component's view ( or many other options )
Lets's take dj-classifieds component that is implemented on the demo website of dj-real-estate02 template.
The dj-classifieds component is assigned to "Home" link of the horizontal menu, where "Home" link is a default link item with Itemid = 1.
DJ-Classifieds uses that Itemid to display ads, so the single item of the particular ad is displayed at the front page.