I am not sure if my post title is perfect about what I want to express đ , let me clear. When we hit any link in joomla that must load any component with modules, header, footer … etc so many things. But what we need to do  if we want to load only the component part ? Ok if still you are not clear, then go to your template index.php file and check what you do with the following line
[code]<jdoc:include type="component" />[/code]
Yes I am talking about how we can load only the component with any link that the above line does. let you are in a link in your site for com_content, for me now I am in that link in my local test site. http://localhost/jtest/index.php?option=com_content&view=category&layout=blog&id=1&Itemid=50
If I go to the link I see full site. Ok now if I modify the url by appending &tmpl=component at end
http://localhost/jtest/index.php?option=com_content&view=category&layout=blog&id=1&Itemid=50&tmpl=component
I see only the component part. Please try yourself. This is how we can just show the component part. If you check your template folder there is a file named component.php which actually shows if component only link is opens. If that file is missing in your template then find in the system template folder. Also there are another two template files for error.php and offline.php which shows the error page and site offline mode page.
Now let me discuss when you may need to load the component only part. Let’s you want to show something via joomla native popup window, like you want to make popup login you can do this trick. Once I wrote a article about how to make modal (popup window) using joomla native modal javascript library.
Example: go to my joomla demo site  http://idea52.com/old/ click the feedback button, it will load the com_contact component in joomla native modal window.
Thank you.