This is just a question about Invoice Closed

I have just noticed the close Invoice so what does that do exactly if I close an invoice after its been paid does it still show up in a P&L for that year. what is the reason that people use this for ?

Closing an invoice has no effect on the P & L. It greys out the invoice and places it below the open invoices.

Also it doesnt appears in Drop-downs such as on receipt and payments.