Microsoft wants your data.
before you install Windows 10, or at least allow Windows 10 to have access to your personal data, pictures and so on. you need to have a look at this article.
If you installed Windows 10 and like privacy, you checked the defaults, right? Oh dear ? The Register
It seems that if you install Windows 10 and do not .Change your default setting, Microsoft can have access to anything and everything that it wants from you. Emails; photos, Bank account numbers, Credit card numbers, whatever they wants. If it's on your computer they can get it.
Make sure you change your default settings to protect your privacy.