Since securities are issued in dematerialized form, a depository account record is the only confirmation of an investor's rights. A statement fixes the status of this account at a particular moment and is issued by the depositary upon the account holder's request.
A statement is not a security and does not create rights in itself: it merely certifies what is already reflected in the accounting system. Securities cannot be transferred by transferring a statement—transfer of rights occurs only through account operations.
The practical value of the document lies in control. A statement is needed when changing a broker, when resolving disputes, to confirm ownership to third parties, and simply for periodic reconciliation: the portfolio composition in the broker's application should be periodically compared with depository data.