It depends. Effectively using ads can dramatically increase your course earnings, while poor advertising can lose you money.
You should look to get back between $2-10 from every $1 you spend on advertising if you’ve got successful ads. That includes money people pay directly for your courses, as well as any upsells or downsells or affiliate sales from the course too.
If you’re making more from your ads than they cost, then simply increasing your advertising spending can really increase your overall sales!