I'm thinking about taking the Two Weapon Fighting feat. I'm a 7th level unchained rogue with the knife fighter and scout archetypes. So far I've concentrated on optimising my movement around the battlefield, with the Dodge, Mobility, Spring Attack, Fleet and Underfoot (I'm a Halfling) feats. Also my Scout archetype allows me to add Sneak Attack damage whenever I charge. I get have a +11 to-hit bonus with my preferred (light) weapon, and do 1d3 + 4d8 (sneak) damage. I reckon I do on average
0.6 * 24 = 14.4 damage to an opponent with an armor class of 20
If I take TWF, my to-hit will drop to +9. So I'll do
0.5 * 24 = 18 doubled = 36
So taking TWF seems a no-brainer. Are my calculations correct, and are there any other factors I should take into consideration?