GLAs when used on an Incident behave slightly differently than on other Service Desk Items, such as Service Orders.
The GLA on the Service or Equipment will be pulled into the Incident by default.
Changing the GLA will allow for any Labor or other Non-Recurring Charges to be Billed to a different GLA than the default GLA on the Service or Equipment.
Completion / Finalization of the Incident will NOT alter the GLA of the Service / Equipment.