If the theft occurred in 2017 or earlier, the deduction can do more than reduce your 2017 tax to zero. A large theft loss can produce a net operating loss (NOL). An NOL resulting from a theft loss can be carried back 3 years, and then carried forward up to 20 years or until it is used up. So it can reduce your tax for previous and future years as well as for the year of the loss. The rules and calculations for a net operating loss are very complicated, and TurboTax will not do the calculations for you. You should definitely consult an experienced tax professional to look into the possibility of a net operating loss.
As others have said in the comments, if the theft occurred in 2018 there is no deduction, and it therefore cannot produce an NOL.
