It's not even close to free. It's X% cheaper where X is the tax rate the company is paying.

eg.

$10,000 in gross profit - 20% in taxes = $8,000 net profit

$10,000 in gross profit - $1,000 rent = $9,000 - %20 taxes = $7,200 net profit

The net rent was $800 instead of $1,000 but not free.