GL Reload is a status used to "Reload" the GL Entries.
When you set to this status, the invoice re-opens, however it is not visible in the email batch wizard. Any invoice in this state will not be synced to your accounting package.
When you close the invoice; by setting the invoice back to a closed status like "Closed - Emailed" the invoice will generate the new GL Entries based on the GL Account mappings at that time (ie once you have made a change), and can be sent to your accounting package the new mapping.
During onboarding it can be useful for invoices in an Un-Batched state (not posted to accounting), to be set to GL Reload while a review of the GL Account mappings is being reviewed.
Once the GL mappings are confirmed as correct; all of these invoices can be changed en-masse.