How safe is to give your personal information on websites

 How safe is to give your personal information on websites such as facebook, my space and any others? What’s the limit for you?

  In my opinion is so unsafe give my personal information to big platforms  because you are giving information very important with which know your  identity, with him tthe platforms like facebook, twitter,etc.  Can make advertising campaigns made expecifically for you, and in another theme  exist persons who use your information to make a scams which in involves you  in many problems how can it be with the justice.
 In specific anything person can know tinghs  personals with only enter to my profile. The internet is a place with a millions of peoples and us don't know his intentions.
 If I have put a limit would be a generic information not than personals things.