Powering snowballs with glowstone makes them heavier. If you use double glowstone and TNT, the snowball is so heavy you have to throw it at maximum range and duck back to survive. Anything nearer and you're toast. Lesser amounts of glowstone cut down the range to a smaller extent, double glowstone is the one that's tough. It's not linear with sugar/cake, cake will still get you much better range.