Required or . . . Crank/converter bushing

You didn't say what years your engine and transmission combination is, BUT-
The only time you need a convertor bushing is when you're mounting a '67 and earlier transmission/torque convertor to a '68 and up crankshaft.
The convertor noses changed diameter in approximately the '68 model year, becoming larger from then on. Therefore the crank flange had a larger diameter pocket. Using a early (small diameter nose) convertor on a later larger diameter crank with the larger pocket would supply no support and allow the convertor to move, causing all kinds of vibrations and harmonic issues, eventually cracking your flexplate and probably trashing the front pump.
The spacer (it's not really a bushing, since there is no difference in rotation between the convertor and crank, thus not requiring a plain bearing surface like on a true "bushing") makes up for the differences in diameter between the late crank pocket and the early convertor nose.
If you are running a late crank and late convertor, no spacer bushing is needed. If you are running an early crank and an early convertor, no spacer/bushing is needed. Only the early convertor and late crank gets a spacer. To run a late convertor on an early crank, machine work would be required to open up the pocket on the crank flange. Custom convertors can also be used to accomplish the swap in either combination, since factory convertors cannot be swapped between early and late transmissions- the input diameter and spline count changed at that time, too.