on behalf of for the sake of 的区别

题目

on behalf of for the sake of 的区别
这2个短语都有为了……利益的意思,当然on behalf of 还有代表的意思,我想知道2个短语意思为 为了……利益的区别,比如 i testify on behalf of sb,我为了他去作证,i testify for his sake.这2句话有什么区别么?
or i spoke on behalf of the plan ,i spoke for the sake of the plan 有什么区别？

答案

i testify on behalf of sb 我代表某人去作证,
i testify for his sake 我为了帮助他而出庭作证,