The Overdraft tracker is a great way to grow sales. It provides an "evidence-based" approach for the sales team to discuss options with customers and upsell them to new revenue tiers (if that's your business model).
If you have hard limits on paid licenses, as most vendors do, you will never see any latent demand. The overdraft tracker allows you to add a new limit to each license to enable the user to consume more up to a higher set limit (so you still control the overall usage).
When they consume more than they paid for, they go into "Overdraft," you can easily capture those users/entitlements in a report and use that at renewal time or for sales, in general, to contact your customers and sell them more based on your policies.
This function is a premium option on the entitlements setup, reports, and activity log pages.