The Gurus said sims will be more drawn to interact with sims they are Attracted to. So if you send a single sim to a Bar, for example, and let them run on autonomy, they should auto chat with more likely prospects than previously. Take note that things like being in a relationship, friendships and family relationships also increase chance of interactions, so it might be harder to notice if they are there with known sims.
Attraction between two sims makes romantic relationship easier to build so the relationship bar (pink bar) goes up faster. Whether this is down to them just enjoying interacting with them more and gaining more relationship from it, or success rates of interactions due to the Attraction, I'm not sure. Lack of Attraction has the opposite effect, making romantic relationship increase take longer.
Basically, you can still romance anyone with the relevant Gender Prefs, but the more Attracted to your sim they are, the easier it will be.