Is there any in-game 'benefit' to building a relationship in the game? I remember in Dragon Age (can't remember which) you were awarded special player synergies, so that was useful. Of course, you need to keep your other party members happy enough to remain (if you want them), that is a given - but the relationship stuff is more often than not something I find a chore...unless there's some reason to pursue it, like a perk that increases your effectiveness....
Sure there is, the effect that the relationship has on the story. I plan on romancing every companion eventually, because I want to see how the story twists.
I plan to play origin characters and see what weird romances are possible (SH & Lae'zel?). I suspect there are a lot easter eggs to be found