What was the advantage of a rotating crops medieval europe

I believe the answer is because it makes the soil more fertile

Rotating crops every year makes sure that whatever crop is being planted gets the nutrients it needs from the soil.

Explanation:

The soil is being run dry of a certain nutrient because it is being taken by whatever the crop is. If you rotate the crop for the next year, those nutrients will replenish while a different nutrient is being taken for use by the new crop.