I hope I understand the question correctly. I know the method is called time-proportional temperature control, but I think it is the same thing.
Essentially, in one approach you can have a phase-controlled SCR or triac, that adjusts the voltage (and hence the power) of the heating element. The problem is the relatively high EMI because the triac or SCR turns on rapidly, somewhere in the middle of the AC cycle.
But you can also turn on the triac at the zero-crossing of the AC cycle and keep it on for several cycles. When it needs to turn off, the triac will turn off again at the zero-crossing and will stay off for several cycles.
Thus, the AVERAGE power delivered to the heating element can be adjusted by the number of full cycles it is on, versus the number of full cycles it is off.
This is time-proportional control. Since it always turns on the heater for complete cycles, I think it is the same as the one you mention.
The advantage is lower EMI and lower current waveform distortion, thus lower harmonic content (because the current will closely follow the line voltage when the triac is on and will be zero when off, instead of being a chopped sinewave). That means a higher power factor.