If you are controlling the pulse width then not using a DC restore circuit will mean that at a high value of duty cycle, the peak voltage from the transformer will not be enough to properly turn on the MOSFET. This is because the output of a transformer must have an average value of 0 volts and if the original pulse shape is 10 volts for 90% of the time, it will become 1 volts for 90% of the time after the transformer.