Convincing a customer to order early from your store can shift that order from a competitor.
If a customer hasn't decided where to place their order or they are shopping around, you can win their order by having your Black Friday deals early. Especially if your competitors sell the same product or a close substitute.
That customer might now buy from your store in the future, depending on your Repeat Purchase Rate (found in various reports in Repeat Customer Insights). They won't even consider a competitor if you stay top-of-mind (you market to them) and your prices/benefits are close or better.
This doesn't work in all industries, but it works in enough of them to be worth trying and seeing the results.