Explanation
A manually created reservation is a document that reserves a certain quantity of a material for a specific purpose or account assignment object. Some properties of a manually created reservation are:
You can assign different account assignment objects per item, which means that you can allocate the costs for each reserved material to a different cost center, order, project, or asset.
You can set the Movement Allowed indicator per item, which means that you can specify whether you want to allow goods movements for each reserved material or not. References: SAP S/4HANA Sourcing and Procurement | SAP Learning, Course S4510, Unit 2, Lesson 1.