The budget upscale parameter option gives you more freedom to have more difference between the spend and the budget of a campaign/adset.

To use this option and set your threshold, you can go to the Automation form of an existing Automation or create a new Automation, go to the Budgets & Schedule step, and toggle the "Advanced Mode".

With this threshold, you can set how much difference there can be between the budget and the spend. On default, the threshold is 20%. If you set it higher, this means that there is more room between the budget and the spend before it will downscale.

For example: If you set it to 100%, it will take 100% of the spend compared to the budget.

This option gives you more room to make your own choices regarding the Automation form.