Sometimes I just use the formula "A+B" with great joy - wondering why the meta mixer doesn't seem to be able to do this.
Also I've once made the formula device help in pretty exact keytracking frequency parameters like filter cutoffs after taktik published some info, a recovered version of the thread seems to exist here:
Yes, I've been a little confused when writing this, and should finally get around to making a tool that will auto setup the stuff.
But you get the point, you can map from one parameter world into another, sometimes better than with the default 5 curves.
Or combine 2 or 3 parameters in some way. Or like the inertia devices, smoothen parameter updates, which is especially useful when you use pattern data commands to control then-smooth automations. Nerdy stuff like this.
Also I have managed to make synthetic pattern effect commands with formula devices. Like forging xy commands, for example x=speed and y=depth of an lfo or the like - and tune it to behave exactly as you'd want it to.
Together with hydras and lfos you can get pretty crazy logics of modulation operations.