It's more social when there's achievements. I won't lie its a bit bragging-ish but its also a way to show how skillful you are to the world (most of the time).
I only try and get ALL the achievements for games I really enjoy and like, such as this one. They go hand in hand with great games for me. It feels like you've done everything when there are goals in place with achievements and you 100% them.
I also don't buy that BS of making your own goals in games. No one will know or care you did it except you (such as using level one characters or default equipment all the way through).
With achievements its universal and people will either have unlocked them or not. It's a measure of how much you like the game and how much you have invested your time into it and where you stand against others. It's almost a competitive metagame in its own right. Especially with long games like this.
Basically it almost feels like I'm doing a disservice if I don't get all the achievements for a fantastic game like Dragon's Dogma, Final Fantasy XIII or Skyrim.