Hi,
In general i agree with the above.
However if extension is required, then it should be able to be obtained if at all possible.
Perhaps the problem lies in a motor control issue where extension is not controlled properly and so a change in motor pattern might be helpful.
I have used this on people who had pain standing in erect neutral but a change in muscle usage and patterning into extension resulted in being able to hang washing on a line above head height without pain.
Shirley Sahrmann has a good but difficult to read textbook on movement impairment syndromes and Peter O'Sullivan has done some work in this area as well.
Good luck!