[SmG Conan]

well, minecraft saves what happened in that chunk so it can be loaded later. I mean, you're in
x 100 z 150, and you make a 10x10 hole. Later, you move to x-780 z-890, make your house there. After that, head back into the last coordinates x 100 z 150, and you will find the hole.

Minecraft needs to save every chunk. The reason why it doesn't not load "all" the chunk just one time, it's because it will take like 1 hour(probz more) to load them all.