These things have been discussed previously in different threads on different forums. Firstly, there is the ability to trade territory, rather than just selling provinces. This may be a player-only feature if it's too hard to get working with AI, but the general idea is to be able to have mutual territorial concessions, either as part of a war deal or in peacetime with exchange of money. I often sell provinces to people for 0 ducats, so this makes selling masses of territory more convenient. It also makes it possible to buy a province you want that the AI or another player considers not very valuable for something they might consider valuable. I'm not sure if this has any kind of historical basis for the period, but it's something I'd like the ability to do, as a player.
The second thing is the ability to "liberate" provinces as in Vicky 2 - returning them to somebody with cores on them. Somebody who might be in the war, or might not. Generally, if you've sieged a province, then only you can take it in a peace deal. Deliberately not sieging provinces so my vassals can reclaim some cores is inconvenient, I'd rather just be able to give it to them straight away. I can just take the territory directly, but then I have to sell them, one at a time, which is a bit tedious.
The second thing is the ability to "liberate" provinces as in Vicky 2 - returning them to somebody with cores on them. Somebody who might be in the war, or might not. Generally, if you've sieged a province, then only you can take it in a peace deal. Deliberately not sieging provinces so my vassals can reclaim some cores is inconvenient, I'd rather just be able to give it to them straight away. I can just take the territory directly, but then I have to sell them, one at a time, which is a bit tedious.