[RadioKid]

With "YO" at the end, the sentence will have meaning of "I ask you"or "accept it". In a sense, it is like "please". I'm not sure it makes the sentence stronger. Rather, "YO" adds "I told you" or "as you already know" to the sentence. It shows the more strong will and makes it more reasonable (not by force or threat).

And note that when you add "YO" after the action of yourself like "MATSU:wait", it means "MATSU-YO:I will wait".