Likes and Dislikes give additional social options. Sims can and do discuss these things autonomously. I've seen them ask about a favorite color or a hobby, and discuss their favorite music. When two Sims liked the same thing, they got green plus signs which boosted their relationship. When one didn't like what the other one did then I saw them get red negative signs and their friendship took a slight hit.
So far, the Likes and Dislikes developed by the Sims that I play have been pretty much on target with their personalities. Unfortunately, the same can't be said about the game assigning Likes and Dislikes to unplayed Sims. For example, in a game that I'm playing right now, Duane Talla who's always at the gym, reacted negatively when my Sim enthused about Fitness. It turned out that the game assigned Duane with Dislikes Fitness. Since I don't play Duane I don't know if he was tense the whole time he was at the gym. He seems to be programmed to be at every gym in the game just like the mermaids. My Sims generally like Fitness and will go to a gym once or twice a week. I guess Duane is doomed to be tense in this game because I don't play pre-made Sims.
I think that Likes and Dislikes are a decent start for something that I hope gets expanded. They provide Sims with more options when socializing besides the same old topics. I have Sims unlock the Grilled Cheese aspiration and Herbalism skill just so they have extra things to chat about. I have two Sims that like Fruitcake. I've seen them chat about Fruitcake with other Sims. Sims with the Foodie trait usually react positively to this topic while other Sims are either neutral or positive.