As a rule in accounting, everything must be accounted for. That also includes prepaying for something you don't yet have possession of or actually own. Look at some examples any you will understand.
- Inventory purchases receiving: A liability account used to prepay for goods not yet in possession.
- Customer deposits: Deposits from customers for goods not yet sent to the customer.
- Retainer: Prepayment for client services not yet provided.
- Prepaid rent: Rent paid in advance.
All of these accounts are required to be recorded as the transactions come up. As they are recorded, other accounts will be used to offset them and eventually will zero out once the goods/services have been received/shipped/or performed.