Here's an example of what your taxes would be on a property with $50,000 taxable value which did not claim a principal residence exemption, compared to the same property with a principal residence exemption:
$50,000 Taxable Value
Times 39.58 Principal residence Millage Rate
Comes to $1,979 Total Tax Bill for 1 Year
As you can see from this example, it is very beneficial to file a Principal Residence Affidavit for your principal property!