Can removing the catalytic converter mess up the cars computer or Ruin gas mileage?

Can removing the catalytic converter mess up the cars computer or Ruin gas mileage?
A catalytic converter's function is to filter most pollutants out of the exhaust so it probably wouldn't mess up the computer in the car or lower gas mileage.On an OBDII vehicle(post 1996) the computer watches the O2 sensors to monitor converter efficiency If the converter has failed(or is missing) the computer will adjust fuel ratios to try to compensate This can ruin economy,