What is the benefit of building ROS from source?

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I'm just wondering what are the benefits of installing ROS from source, compared to installing from pre-built binary with sudo apt-get install ros-kinetic-desktop-full?

My general understanding is that people build a library X from source because they want to:

• customize the library X itself
• or because they require new features from the lastest version of other library Y (which they want to build the library X with)

Question

So my question is kind of two-fold:

1. What are the benefits of installing ROS from source, as opposed to installing by sudo apt-get?
2. If my understanding above is correct, how do we build ROS library with newer version of libraries such as pcl-1.9, boost-1.70, vtk-8.2.0 or OpenCV4?

Example

For example, when I try to build ROS from source (as in the manual), it asks me to install libqt5 even if Qt5 was installed already (built from source and use in other project). How should I tell rosdep to skip this, or pass Qt5 path to rosdep (similar to the way we pass CMAKE_PREFIX_PATH to CMake)?

w@laptop:~/mylib$ cd ros_catkin_ws/
w@laptop:~/mylib/ros_catkin_ws$ rosdep install --from-paths src --ignore-src --rosdistro kinetic
executing command [sudo -H apt-get install libqt5widgets5]
[sudo] password for w: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  cmake-data libjsoncpp1
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  libqt5core5a libqt5dbus5 libqt5gui5 libqt5network5 libqt5svg5
Suggested packages:
  libqt5libqgtk2 qt5-image-formats-plugins qtwayland5
The following NEW packages will be installed:
  libqt5core5a libqt5dbus5 libqt5gui5 libqt5network5 libqt5svg5 libqt5widgets5
0 upgraded, 6 newly installed, 0 to remove and 18 not upgraded.
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