The Vault allows members to hold an item for an indefinite amount of time. That is, Full and VIP members can use their slots to hold item in their vault until they are ready to purchase. You can rotate the item in your vault as often as you like. The idea is that this allows you to have an item available to you until you are ready to pay. You do not have to commit any funds in order to place the item into your vault, other than your normal membership dues. However, if you do not pay your membership dues for a given month, the item will be released back into stock and made available for purchase to everyone.
VIP members can even place the items from exclusive sales into their vault. This allows for maximum flexibility for securing the genetics you need!