Question

what are the advantages of the fact that most reflex action are governed by spinal cord?

Answer 1

Tha the response is very quick

Answer 2

There are many situations which require immediate action without thinking about it  for long,  in order to prevent further damage such as removing our hand on touching a hot object. So, in such situations, rapid reaction can be obtained by sending signal only to spinal cord and getting the response from it fastly. ​No time is wasted  by sending signal to brain for filtering and analysis in such situations. Such involuntary actions are called reflex actions and they are governed only by spinal cord.