Privacy

Often hosting and registration companies that are cheap, make their money by selling your email address and other private information.

You may say "I don't have anything to hide; my email address is not important."

But these days that kind of information can be a way for hackers to get in to accounts, for governments and corporations to mine information, with results that may not happen to you, but to your contacts and friends.

And besides that, it is just plain rude and unsocial to collect people's private information. Do you do business in the every-day world with people who are rude and unsocial?