For the sake of argument: o que isso significa e onde usá-lo?

One day, you're talking to your friend about a mutual friend of yours. You think he's been cheating his wife with a woman she met at a party you all went to. You're worried about what's going to happen to his family if his wife comes to know all about the truth. You wouldn't want your friend's family to destroy over such a silly adventure you guys had the other night. Especially because there's a child involved in the story. The friend you're talking to doesn't understand how bad of a situation that is and doesn't pay too much attention to what you're saying. So as a way to make him think, you say: Assume, for the sake of argument, that his wife finds out about that woman. What do you think is going to happen to his family?

When you say for the sake of argument, you're considering a possibility. In that case, the possibility is that his wife would find out about his husband's new affair and his family would be destroy. That's something to worry about. You, as friends, should give him advice and tell him to forget about that woman and go back home to where he's always belonged. It's not worth it to throw it all away for a night-strand. That's it for today guys. Take care!