When I run a game, I admit, I am hesitant to kill PCs.
Usually part of this is due to the fact that I want the players to really dig their characters, put a lot of effort in to them, love playing them. They're NOT just a piece of paper or a pawn on a chessboard.
That said, I want their experience to be fun, scary, with a constant threat of danger and possibly even mortality.
If a PC is to die, I really want it to happen in a meaningful way if at all possible (though in a grim Dark Heresy-kind of game, it's perfectly understandable for even a PC to die in a meaningless way...it's the nature of the grim future).
I tend to build up NPCs and get the PCs close to them, but I also have a tendency to sacrifice them for the sake of a dramatic scene.
PCs though, unless they are patently stupid and doing what they know will likely result in death...I probably won't let them die.
Part of this is that in my games, I hate the idea of protagonists and antagonists fighting to the death every time a weapon is drawn. It's just ridiculous. When things look grim for the antagonists I'll secretly roll to see if they cut and run. Live to fight another day. Recurring bad guys. Unless the antagonist is mindless like a zombie or skeleton or something...it'll think twice about staying in the fight after half his buddies get smeared all over the room.
I expect the PCs to consider this as well. Not every encounter is designed to be "won". Sometimes the PCs wander in to the Bad Guy Home Base and realize they are woefully outgunned and need to RETREAT!
I guess it comes down to choice.
I try and give my players and their characters lots of choices, and with this comes a lot of rope to hang themselves. I try to be really up-front about what characters notice: give them plenty of chances to realize what the situation is and if/ when they get in over their heads.
They set the stakes and if they choose to bid high, or go "all in" then they CAN die and I won't be as forgiving with the rolls. I won't however sneak up on them and blindside them with situations they will not be able to get out of. They might get snuck up on with a situation out of their league, forcing a retreat...but they have plenty of "outs".
In order to do this...sometimes I fudge rolls.
I also roll my dice all the time out of habit, so only half the time it's for a purpose. I also call for lots of random rolls that mean absolutely nothing. Especially good or bad rolls on either side of the screen can have an impact somewhere.
So how do you guys do it? What are your thoughts on killing PCs and fudging die rolls?