In Vanilla Minecraft, you can just stand still and essentially live forever if no mobs or players interact with you, which never made much sense to me. This mod simply makes the hunger system a bit more realistic by depleting the player's hunger level even if they're not doing anything, and it accomplishes this by increasing the exhaustion level every tick. This is also a way to discourage afk-ing in a server.
By default, exhaustion is increased by 0.001 every tick, which translates to half-drumstick depleted every 200 seconds, but this can be changed in the serverconfig.
If you don't know how exhaustion works, here's a quick rundown:
Whenever the exhaustion level reaches 4, it gets reset and 1 point (equivalent to half a drumstick) is subtracted from the saturation level. If saturation is already 0, then it will subtract 1 point from the food level instead.
You can read more about the hunger system in the Minecraft Wiki.
Use the mod AppleSkin to see (in-game) all of these mechanics in action.
