Why enter fair mkt value along with land + improvements from tax bill while Converting primary home to rental

Hello,

 

I bought my home 10 years back in $300,000. I converted it to rental last year. Fair market value of the home at the time of conversion was $600,000.

 

I am using Turbo Tax Home & Business. When I enter rental information, it is asking to enter property’s purchase price, remodeling, Fair mkt value, and Land value & Improvements from tax bill for the purpose of depreciation.

 

What is the purpose of entering the fair mkt value when land value and improvements from tax bill are also to be entered? How are these used?

 

Thank you