I started my SW leaning towards LS but quickly gave up and went DS.
LS choices feel just awkward, out of place. When you choose to spare someone all you really get is a confused look and a line like "wow, I never knew a Sith could be merciful".
To spite Baras? When he hears about your carebearness all he does is shrug and say "whatever. You're still my walking weapon of mass destruction". And that's the truth: no matter what you do you will always be perceived by NPCs as Death incarnate, the destroyer of worlds. Regardless of the fact that in private you are just a soft-hearted pansy.
EDIT: plus, turning Jaesa to the dark side is just awesome. To rub the Jedi's utter failure on their self-righteous faces, stealing their most prized student right from under their noses...