For when you want to use something that is very physical to destroy other things that are physical. Works best against: Everything.
#RailgunsFTW
The simple fact is that an energy weapon could not ever have the stopping power as a kinetic weapon could. If you want to destroy something, if you want to blast it apart, you use kinetic. If you want precision, and cutting someone's heart out from three kilometers away without destroying anything else, use a laser or phaser or whatever the hell.
But if you want something
DEAD, you use a high-velocity railgun.