It really depends but generally speaking just because of the mechanics of it voice-over is easier because there is no hair no makeup no wardrobe no fittings no line memorizing. You don't have to me woken up in Russia at 6 in the morning and go film a scene. It's just easier on the body the family life to do voice-overs.
Everybody has a job to do. There are people in Iraq on both sides of this war who do what they do for religious reasons and they feel with God on their side. Some people are good at annihilating people. Maybe that's their gift.