I don't completely understand

the Principle. Is it to live in complete obedience to the Prophet, or is it ultimately for procreation?

If it's complete obedience to the Prophet, the first being Joseph Smith, the Mormon Prophet who first delivered God's directive that Mormons practice plural marriage in 1830, would each successive head of the church be considered the Prophet to whom the members give their obedience, ot is it still to Joseph Smith.

Is the Principle itself for procreation purposes only? How can individual members decide to take multiple wives while others decide not to take individual wives? If members decide not to take multiple wives wouldn't that be construed as not being obedient?