I think it is very useful, from remembering birthdays to be able to create events in the easiest way, also knowing that most of the people you invite will see it, contact family members long lost to you ( this actually happens a lot, i have a very big family and every now and then i find somebody i haven´t heard of in a long time ).
You can make this very enjoyable with the right settings, like, i don´t like my mom seeing me drunk, nor on facebook or in real life, so i don´t show her those photos, just as i don´t get drunk in front of her, is kinda the same principle.
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