FastEddieLB wrote...
Completely ignoring the rest of the thread to answer the OP:
Advantage: You get to have that obnoxious crybaby Alistair executed! =D (That was the highlight of my first playthrough)
Disadvantage: None, really... unless you actually want that sissy to be king.
If you spare Loghain, one of the first conversations you have with him you can say, 'You cost me Alistair you know.' And his response is, 'And you can thank me for that later.'
Persephone wrote...The Warden administers such justice and MERCY a few times? Really? If this is MERCY, I'd hate to see.....well......GOD, I simply cannot understand such a butchery. 
I dug this quote up because I like a challenge. I believe you are asking how death can be considered a mercy for Loghain? Very well, I accept! Let's see...
Consider that Loghain has sacrificed his entire life in devotion to protecting Ferelden. He has put his duty before even his own humanity. The life he has lived has never been his own. Now consider that his actions in the game actually serve to condemn the very country he was sworn to protect. Every decision he makes sows more dissent and destruction. But it is his duty to protect Ferelden, he cannot falter, he cannot stop! So he pushes ever onward with his doomed course of action because only he can save his country!
Finally, at the Landsmeet, he meets his match. He realizes that Ferelden has a savior (with the strength of Maric) in the Warden. Finally, there is someone else who can carry the burden that he has shouldered for so long. I personally could not help but reflect on my own life after yielding to the authority of my opponent; they may choose to kill me after all. I imagine that Loghain is realizing that he has never really lived his own life. Duty has dictated every decision he has ever made. He was forced to abandon any hopes of love or any sort of selfish indulgence. He favored rationality over humanity, and after all of that someone else came along to succeed where he failed. I couldn't help but wonder if it was all a waste. He must be completely spent at this point. Rest would be welcome. I'm willing to grant him that rest. And should someone come to challenge me for my actions, I can only hope they are half as admirable a man as Loghain himself.