title: What install command does in cmake?
body: <p>I am sorry for being so naive. I tried to understand from this cmake website's <a href="https://cmake.org/cmake/help/v3.8/command/install.html" rel="noreferrer">link</a> But could not understand. I have a sample cmake file, where an executable is generated by </p>
  
  <blockquote>
    <p>add_executable(${PROJECT_NAME}_node src/filename.cpp)</p>
  </blockquote>
  
  <p>Then later it installed by the following command </p>
  
  <blockquote>
    <p>install(TARGETS ${PROJECT_NAME}_node ${PROJECT_NAME}<br>
     ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}<br>
     LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}<br>
     RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION} )</p>
  </blockquote>
  
  <p>This cmake is from ROS so catkin is there. The overall question remains the same. Does someone know, why do we need to install TARGETS/ FILES?</p>