Is all about GM & Players style. Say you've planned and entire quest line, but instead of helping the Paladin save his friends, they decide to kill him, ask for a reward from the Dark (Under)Lord and then masscrate the village in tribute. Should they not get Xp and stuffies from doing those things? "No", says the man at Obsidian, "only my premade quest and ideas should reward players"! I know games have their resource limitations, but I'm not asking for this new plot, just that killing the Paladin is interesting and rewards my effort/idea. Probably huge quest will have this outcome, but I like to be able to do it at any point in the game, with anything... if not the items & subplots, at least some goddamn XP for killing a paladin, ffs.
And games like Baldur's Gate allowed both playstyles, you could follow quest happily and Mr. Designer would be very pleased, or you could go on a rampage and kill everything and still get interesting things and no one would shout "you're playing it WRONG!" Long story short, Sawyer would ban me of his P&P game before I've even made the character sheet.