The customer also receives different order ids if they have purchased multiple items.
When a buyers place an order with multiple items in the cart then, separate order ids will be generated.

Separate order ids will be generated at the back-end if there are multiple items in the shopping cart
Separate order ids will be generated in the back-end as well when a buyer place an order with having multiple products in the cart.

Separate invoices and shipment can be created for individual order
The admin can create separate invoice and shipments for each individual order id generated by split order.

Customers get detailed information about each item of the order placed
When the order splits into different order ids as per the items in the cart the customer gets more clarity and understanding about the items purchased.