Don't give your cell phone number to Google, when they ask for it 'for your security'. They can use that to find out who you are, by matching a phone listing to a name, and cross reference that to e-mail addresses, and Facebook or other social media, where one's real name is used, but the links to internet handles/ e-mail addresses are indirect. Using Google World, your every move can be tracked by Google, as long as you are carrying a cell phone on your person.
Don't give any website information about you that they don't need to know, just because they ask for it. You have no control over how they will use that information, or to whom they will give, trade, or sell it, either now, or in the future. Most people just give that up, because 'they have nothing to hide'. They'd better hope that they'll never have anything to hide, because once you give them that, you can't take it back from them. They own a part of you, and they won't tell you why they want to know so much about you, in exchange for giving you something shiny.
Think about the guy in the grocery store, who wants to offer you a ballpoint pen or a Toronto Star, if you'll sign up for a credit card. All you have to do is give him authorization to check your credit history, and you get a pen, or a paper. Once he has your credit history, even if the credit card is not approved, he can sell that information to other people, who want to know your credit history. They don't give you anything, but you've given them indirect authorization to share what you gave, to anyone who wants it.
The police would like to have every purchase made with a credit card, and so would the government. Many merchants will give a discount on HST, if you pay them in cash. If you ask them, they will say no, but if you pay them in cash, sometimes they will just apply the discount, and encourage you to pay them in cash for your next purchase. Your Escort might cost more, if you were forced to pay by credit card. Would you want the guy in the grocery store to be able to find out everything you spend your money on? If not, say no to the pen or the newspaper, and let some other chump give that information away.