With it, a listing can appear in Google with its price and stock status, and in Google Shopping's free listings. Without it, the product is a page like any other.
For a Ghanaian store the currency must be GHS and the availability must be kept current, since a rich result showing an out of stock item as in stock is worse than none. Our online store builds generate it from the product record.
The same record that renders the page produces the schema, so the two cannot disagree, which is the failure mode when schema is added by hand.