15 year olds definitely want to have "compatibility with different systems" including the source of their pay packets, allowance, and access to resources - ie old people and their old email.
But it turns out email, even if used infrequently, is still important. It's easy to have multiple accounts sit there indefinitely. Not controlled by one fatcat pulling privacy strings and strategizing your online activity.
Meanwhile another million blue 'f' logos are printed, each destined for a shopfront window, cash register, door. Beckoning the registration and sign up and sign over of your stuff. In return, FB tells a few advertisers about you and your stuff. And FB also reserves the right to build the mechanics of your social communications, private and public, the particulars of which will be in accordance with Facebook's sole decision and strategy in an advertiser-hungry world... And other things without notice and so on.
To be clear, Facebook doesn't tell any advertisers any information about any users. Advertisers tell Facebook what kinds of people they want to see their advertisement, and Facebook shows the advertisement to those kinds of people.
I am always amazed at how poorly personalized facebook are for me or my friends. Basically it's always made of 60% "meeting someone from the area" aka some shaddy semi-porn website.
I am really curious of the efficient of advertisement on FB. I know some large brand (GM I think?) pulled off FB because they did not see any ROI.
I wonder if it holds true worldwide and for smaller brands...