basically, it shows them as your friend. that's essentially it.
oh, and it becomes easier to stalk.. i mean see if that person happens to be online at the time since you can look at your friends list and see if the icon for online is lit or nor (rather than finding a post from them and looking for that same icon).
beyond that, i haven't found any tangible benefits - just a "hey, i'm friends with so and so" type thing