IME the env modulations are very necessary. I didn't use much of the distortion circuits before I started tinkering with the modulations, before that I only used the heat's filters and eq.. Or I used the clean boost and enhancement a bit, but only very miniscule amounts - Adding a significant amount of drive irritated me no matter the circuit, sounded too stiff somehow..
env modulation targets such as drive, wet/dry can be very useful! Even if you intend to only use the heat as a "clipper", with careful env modulation you can coax a dB or two of more RMS without obvious side-effects.