This means you cannot use an exchange wallet as your main wallet, receiving and sending funds directly from it. When you deposit and withdraw from an exchange you must first send to a specific wallet, or sign a message from that wallet.
It has many privacy and usability functions, it's a hassle, and it is done mainly to "protect" the exchanges. At the expense of users, of course.
Viewed neutrally, this could be a good initiative and force users to manage their coins more carefully. Many people still use exchange as a wallet today, which is wrong, and all for the reason of saving a small fee for an additional transaction.