Electric or Mech Fuel Pump? For a carb...

Whats everyones thoughts on pumps? Im new to this, from my understanding, if you keep the magnum front case/timing components on, you would obviously run a electric pump? Or, get the la style case and run a mechanical pump?

And with a electric pump, you would also use a regulator. Just wondering why people go to the trouble of swapping the case to run a Mechanical pump? Something to do with the cam?