In some applications dual IACs will work better to have more balanced flow to all cylinders. Take the Crossfire system that I have on my Grandfather's truck, with the way the TBs are laid out, using both IACs, just like when the system was new, works best.
In a system where the TBI is a single or dual unit more centrally located, you can usually get away with just one.
I mentioned it more to do with how people say you "can only run one IAC," which is simply not true.
Only one TPS would be needed in anycase.