For a manual order, the activity log should show which user created the order, as well as the date and time that the order was created. This allows everyone to know who created the order.
This record is very helpful if there are questions about the order, either at the time the order is processed, or at any later time.
This record could also be a deterrent to a user who might create a manual order and fraudulently claim that the order had been paid when it had not been paid. Once the order was created, anyone in the warehouse could ship it. Currently, there is no record of which user created the order, only the user that shipped the order, so there would be no record of the individual who committed the fraud.
There is already an activity log, and similar items are already logged, so this would be very easy to implement.