I saw few short discussion about this after discovering it, but to me it seems that it is quite a balance breaking exploit.
Briefly, you can harvest all the map without spending a dime.
1. You check when your neighbor field is ready to harvest, so they took care of everything (even contracting you to maintain it).
2. When it is ready to harvest you buy the field. Let's say a 125 000$.
3. You harvest the field.
4. You sell it back for the exact same amount on the spot. 125 000$
So you just got the field crop for free.

Quite a game balance break now since you could live from everyone field for free.
An easy fix from Giant would be to add the value of the crop to the field.
Example:
- The cultivated land (without crop) has a value of 125 000$
- Let's say a full crop of Canola is worth 20 000$ on that field (when fully grown at 100%)
- Then if you buy the field when it is ready to be harvested, you would pay 145 000$ (land + crop value)
- Or If the crop is grown at 33%, you pay 125 000$ for the field + (33% of 20 000$) which would be : 125 000$ + (20 000$ x 0.33) = 131 600$
What do you guys think? Some people will say that you could do this in real life but the reality is that there is a chance that you would not be able to sell the land back. You would also have to pay all kind of fees (welcome tax, notary, real estate agency) which would make the move really risky.
Please Giants fix this. Knowing that it can be done is quite a game breaking hack.
Depending of the forum members feedback, I will report it as a bug.
Thanks!
ps: I did this with grass to feed my animals. I did not check yet if it's the same behavior for all kinds of crops.