This is an approach developed on the basis of good practice. The vast majority of customers prefer to be able to dispose of their funds as soon as they make a deposit and leave the verification issues for when they make a withdrawal out of the exchange.
However, this is not the rule; often verification of the source of the funds is a condition for adding these funds to the user's balance and this happens after the payment operator or the currency network in question has received information about the deposit..
