Why is a full sweep of a cold wallet more secure than a withdrawal? I've seen on This question that you should not make partial withdrawal from a cold storage address; because it could compromise the security of the cold wallet. Can someone explain the related security concerns?
That makes sense to me.

You see, you can generate a wallet completely offline. If so, the private key of that wallet would have never been on a internet-connected computer. That's a safe key.

However, you cannot (as far as I understand) send money without putting the private key of that wallet onto a computer that touches the internet.

Makes sense to completely empty that wallet and create a band new one offline again. Transfer partial money to where ever you want, then transfer the rest to the public key of a new wallet that has never had its private key on an internet-connected computer.