I have a question regarding protectorates in this thread

And here it is;

I am at war with Saxony. When I conquer their only province will I be able to release as a protectorate as I have with Hungary which was an Austrian province?

Yeah you'll have the option to 'liberate' Saxony from their current government to a protectorate government.

Here is a list of all liberate-able countries:

http://www.twcenter.net/forums/showthread.php?t=345757

I remember liberating St. Petersburg into the Russian Empire :/

What is the benefit of liberating a country over just moving in and taking over?

@ crsutton ::
It's self-managed.
It won't rebel.
It won't be attacked.
It can be a buffer state between you and your enemies.
It's a reliable [if weak] ally in a world of backstabber politics.
It pays you half its income.
And it still counts as one of your provinces in game score.

@ BazzBrother ::
No. You can only liberate a province to a major nation when the latter has been obliterated and the region concerned is its capital one. If anything, it should be Moscow.