The benefit of the QBI is elusive indeed. At first glance, it sounds really great - a 20% reduction of profits available in addition to standard/itemized deductions.
However, it has hoops to jump through. First of all, if there is EVER a loss, the loss must be applied IN FULL to the current benefit. However, if a positive result is ever squelched for any reason, the amount lost is NOT carried forward.
Next, the 20% is applied to the taxable profit, or taxable income, WHICHEVER IS LESS. If any benefit is lost thereupon, it is lost forever.
The 20% is a great thing for taxpayers with regular profits, and regular taxable incomes.