Whenever I move through chunks in my world (this is a flat world with nothing in it), i see the CPU of the server rise up, then lower back. To reproduce this:

1.: Create a server with a flat world, without any villages or anything whatsoever.

2.: Join that world

3.: Enable chunk borders (F3+G)

4.: Find a chunk corner, then start circling around that corner. You'll see the CPU rise up.