I have seen both server and client(those in range of it) performances brought to their knees more times than I can count on my hands by people stuffing too many animals in their pens, villagers breeding out of control in a house or similar.
And the absolute worst is when you have a stuffed hopper without overflow.
My server can take a pimped up Infinity mod-pack, with 10+ people having all their high-tech bases running at full capacity, and not break a sweat.
One day, I find my server doing 3TPS with a CPU stuck at a 100% and not budging a pixel. Some Opis later, I found the culprit: a 3x3 fence with 8 chickens in it, a hopper underneath with a chest filled to the brim with eggs. The hopper alone was hogging up 85% of the CPU time and brought everything down to its knees. Broke the hopper, killed the chickens, and usage dropped down again to 20% instantly. And this isn't the first time I had to rescue a server cos of a hopper full of eggs, saplings from a treefarm and such nonsense.
Moral is: When using hoppers, always make sure to have an overflow plan - dense tube trashcan or something - as it can break a server and make an absolute mess for days.