[khaled]

One reason that comes to mind, is to make sure no extra text is inserted in the empty space e.g. after a contract is signed.

[pton_xd]

Signing two copies solves that, or even making a copy after execution.

[mintplant]

Does it solve it, or does it wind you up in court arguing over which copy is the "real" version?

[pezezin]

Easy, just make three copies.

[KetoManx64]

Who gets the third copy?

[fennecbutt]

The government.