Difference between LP & LPA document type in Scheduling Agreement in SAP

Without release documentation (in the standard system, document type LP)
The delivery schedule lines have official character - that is to say, they are transmitted to the vendor as they are saved in the system. The system does not document in detail releases against the scheduling agreement that have been sent to the vendor. Therefore, in the case of the document type without release documentation, the message control facility should be set up in such a way that a message is immediately sent to the vendor if any changes are made to the delivery schedule stored in the system. All open scheduling agreements are always output.

With release documentation (in the standard system, document type LPA)
If you use scheduling agreements with release documentation, the delivery schedule lines are not transmitted directly to the vendor. Initially, the lines of the delivery schedule stored in the system for an LPA scheduling agreement are for internal information only. A message informing the vendor of your material requirements cannot be transmitted to the vendor until you explicitly create an SA release, that is, a forecast (FRC) or Just-in-Time (JIT) delivery schedule. Through this process, you can change the way the schedule lines are represented. With the release documentation, you can display the SA releases (delivery schedules) transmitted to a vendor over a certain period at any time. This enables you to trace precisely when you sent which
information to the vendor.