Why pay for the Notion Freelancer Pack when you could make the documents yourself?
Good question! First things first, you might not need the paid, premium version. Have a look at the free pack and perhaps it's got everything you need. Besides, here's a quick comparison to help you make a better decision.
If your hourly rate is not fantastically small, it might be worth buying the premium version of the Notion Freelancer Pack, to trade those $ for the time it would take you to create templates for: invoices, contracts, timesheets, etc etc.