Some tech:
After the ECU sees a crank signal it uses the previously computed engine RPM (based on the time/distance between crank pulses) to compute the time for the next ignition pulse.

At a steady RPM this was never an issue, since the new RPM will match the old RPM. But during acceleration the computer is, by definition, late in it's timing calcs. In days of slow computers this caused a slight transitional retard only during rapid acceleration. So basic physics suggest that the more crank signals you have, the more accurate the ignition, but with today's ECUs, even 4 pulses per rev is usually more than adequate.