Many networks make money by analyzing and selling your interactions on their networks in order to target advertisements at you with greater accuracy. diaspora* does not use your data for any purpose other than allowing you to connect and share with others.
Choose your audience
diaspora*'s aspects enable you to be specific about who you want to share with. You can be as public or as private as you want. Share a funny picture with the whole world, or a private message with your confidants. You are in control.
Be who you want to be
A lot of networks insist that you use your real identity. Not diaspora*. Here you can identify yourself as you choose, and share as much or as little about yourself as you want. It really is up to you how you want to interact with others.