The grain shape is used to control speed, sharpness and grain. T-grains are very fast because they are flat and present a huge surface to the light. Cubes can be made very small and are used in papers and in print films for fine grain and sharpness. There is a use for every type of grain, even if it is to be a foundation to grow another type of crystal.
You could make a cube and then convert it to an octahedral shape by growing something over top of it. This would then become a core shell or converted emulsion.