Various Types of Orthodox Ordinations

I've recently learned that there are three different types of ordinations that an orthodox rabbi can have. I'm sure I'm not the only one who didn't know and would be interested. Can someone explain why we need three different kinds?

Yoreh Yoreh
The usual ordination is the "Yoreh Yoreh -- He may guide, he may guide". A conjugation of the same word as "Torah". This is minimally mastery of Yoreh Dei'ah, the section of the Shulchan Arukh on kashrus and laws of sexuality. Most ordaining schools won't send someone out to be a rabbi without his also knowing Orach Chaim, the daily laws of prayer, Shabbos and holidays.

Yadin Yadin
A judge gets a second ordination, "Yadin Yadin" (He may judge, he may judge). This shows qualification in the laws of courts and monetary law in the Shulchan Arukh Choshein Mishpat. Since, unfortunately, much of court business nowadays is divorce law, many yeshivos require knowledge of that as well.

Rav Umanhig
"Rav Umanhig" (rabbi and leader). This is someone who is capable of leading a community and answering day-to-day halachic questions, but isn't qualified to be a full "Yoreh Yoreh". Typically this is a teacher, say in adult education, who could use a title to aid his getting his work done.