The point is turning mains 10A on and off at 980Hz is not recommended, generates lots of EMI which will be bad news for everyone in the building as its likely to break-through on every audio device that's mains powered and on AM radios for 100's of metres all around. You'd need to have some good snubbing circuitry to make it tolerable
TRIAC dimmers and motor controllers at 100 or 120Hz are already bad news for EMI, but people are much more tolerant of mains hum/buzz than a 1kHz signal.
For heating you generally use slow PWM (0.1Hz or lower). Preferrably zero-crossing synchronized (some SSRs support this). Thermal timescales are measured more in minutes than milliseconds. For instance standard thermocouple bang-bang control of heaters is effectively slow PWM.