Advantage of using Ros Controller

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I'm little confused about the benefit of using ros controller to control the robot. For example if i can control a servo motor/read encoder directly from a code with ethercat programming, than why should i use ros controllers? And also i'm trying to implement rtnet/soem in hw_interface to control the motors in real time, so if i use ros controllers for high level tasks like sending trajectory positions etc while communicating with other ros nodes like vision node or trajectory planning node will not it affect the real time operation in any way?