As a service provider we do a lot of little jobs and a lot of jobs with a lot of parts. When it comes to invoicing we would love to be able to do a purchase order and create a pool of active parts that we can drag into an invoice without complicating our jobs by creating a project for each one.
So we can go to the supplier and purchase a range of products and then add them to a "quarantine" area. We can then keep track of what's in the quarantine area and if we've missed invoicing anything. Rather than seeing stock items available, as we don't necessarily want to keep "inventorised stock".
This would make a big difference for what we do and a lot of other service based businesses i'm sure (IT, Plumbing, Electrical, etc). Every part that you miss invoicing adds up!