In order to inform them of the fact that an unusual rise in activity and balance is expected and to give legitimacy to it by explaining a reason. This can help

In order to inform them of the fact that an unusual rise in activity and balance is expected and to give legitimacy to it by explaining a reason. This can help prevent some of the automated (or non-automated) fraud detection that can go into place in such situations, ensuring you have access to the contents of that account as quickly as possible.