What does "Enable Multiplayer World Origin Rebasing" do?

After upgrading my project from 4.12 to 4.14 I saw this new option appear, what does it do exactly? Does it allow me to physically go past the 5km5km5km boundary that is considered accurate for physics?
If so, how would that work for physics driven pawns and other physics objects? Would they only respond clientside then or would they still try to be simulated on the server?

I’m asking because my current project requires quite a large world to play in and in my prototype I’ve actually used 20km20km20km - and even there it ended up not being enough. So my current solution is to split the world into individual chunks, each being 1km³, and keeping track of a virtual world origin offset integer value for each actor - thus increasing the total world size from 1km³ to ~214740000km³. This obviously brings weird issues with it, such as handling merging and splitting of players chunks (same or close to the same chunk), getting physics to not behave like a messed up implementation (you ever seen a 140m large object flip out and take out all players? Yup, that happens regularily…), etc.

Note: I posted this here because your forums currently always return an error when trying to make a new thread.

I forgot to mention that due to this limitation I can currently only have at most 9 players on the same server - which is ten times lower than it should allow for.

What? Where is this option? to enable repositioning of the world for multiplayer? Where do I find this option? please answer