This simple exercise is more than just a trapping of mutualistic discourse. It actually forces you to think about their point, and leads to a greater understanding of what they are trying to say... which, in turn, allows you to waste less time by explaining a counterpoint to an argument that they didn't make.
I try to make myself do this even when I'm not arguing with someone. If a task comes to me from my boss, I will do my best to rephrase it in my own words (not verbatim, unless it's something really simple) to make sure we're on the same page.
People who do this in every conversation annoy the everliving hell out of me.
In a philosophical or rhetorical debate, it's an excellent strategy, but in day to day office conversations, ugh.
I try to make myself do this even when I'm not arguing with someone. If a task comes to me from my boss, I will do my best to rephrase it in my own words (not verbatim, unless it's something really simple) to make sure we're on the same page.