On a document line you may only ever fill in three fields. Quick entry makes Enter jump between just those.
Personalise the page (tip 6), click a field, and toggle Include in Quick Entry. Then on that page, pressing Enter (or Ctrl+Enter if Enter is mapped otherwise) moves to the next quick-entry field, skipping everything else. Set it on Item No., Quantity and Unit Price on sales lines and an order is three keystrokes per line.
It is per user, so each person tunes it to their job. Administrators can set it at profile level for the warehouse or the sales desk. Combine with F8 (copy from above) and a list of twenty similar lines takes seconds.