Some wheels will let you mount the TPMS sensor right where the valve stem is on your stock wheels.
Some wheels have a TPMS compatible inner barrel where you mount the sensor on the inner barrel instead of the outer barrel.
The adapter is simply a 3rd way of mounting TPMS, with the sensor on the front barrel, unexposed.
Most forged wheels will use either the 2nd or 3rd method. Which ever forged wheel you order, you can ask the manufacture how they recommend the TPMS placement.