1) it allows people you don't give a rats ass about and wouldn't speak to if you passed them in the street the chance to bore you with every banal detail or their uneventful lives because both you and they have joined in some global "friends" arms races based on numbers of people you've clicked a link for but don't really know or care about
2) it allows you to make even more of a fool of yourself by posting updates and photos of all the oh so clever and funny stuff you did while blind drunk. The kind of thing you'd rather your parents/boss/colleagues/beloved aunt never knew about - except now they will, and probably before you've even came round, because you've "friended" them all on Faecesbook
3) it allows you to look really pathetic by updating your status to "in a relationship with someone I've actually spoke to in real life" after last night's drunken one-nighter only for them to publicly dump you before breakfast.
4) it allows Faecesbook to micro-examine the details of your life and sell all that information on to anyone willing to pay for it. Do you really like being marketed to? Tell Faecesbook what you had for breakfast!
5) it allows some frazzle haired dork who couldn't get laid at Harvard the chance to become a billionaire - and all off the information you so willingly hand over to his sprawling faeces-pumping empire.
Add me to the list of people you barely know on Faecesbook