Mileage plates are for trucks used only part of the year. Depending on the registration weight, the vehicle may log 5,000 to 7,000 miles per year. The truck must have a working odometer or Hubometer to be considered lawful. Failure to have these will result in the revocation of the registration.
Considering an 80,000-pound plate is $2,890, that same plate as a mileage registration is $1,525. That is a large saving if that vehicle is only operated during a certain season and then parked the rest of the year.
If an officer pulls you over, they may record your mileage at the start of the stop, and if they take you to a scale, check to see if the odometer has moved. If the odometer does not work, you will be issued a ticket for no valid registration and overweight on registration citation for the truck's total weight.
For more information; https://www.cyberdriveillinois.com/departments/vehicles/cft/cft.html#mileage
As always The Illinois Truck Enforcement Association is here to help you understand the laws and help keep our roads safe.