From the mailbag: "Is there anything wrong with letting strange people I don't know follow me on Twitter?"
By default, your account is public. Therefore, anyone can follow you on Twitter — just as you don't need permission to follow someone else, such as a celebrity.
But you can restrict who follows you, if you like. You can opt for a private Twitter account, which means followers must first submit a request for your approval before they can read your tweets. Only people you approve can see your tweets and they won't show up in search engines either.
If you've chosen to protect your tweets, you can approve followers from your account home page, profile page or by clicking the link in an email request.
By the way, the Followers link on your profile page or home page will also show you how many followers you have and who they are.
You asked if there was anything "wrong" with letting strangers follow you on Twitter. It does boil down to your comfort level in sharing information, but it's a good idea to be cautious about what you tweet. For example, you might not want to broadcast the fact you're going on vacation for a week, which might invite thieves to your home while you're away. Or you might think twice about tweeting an inappropriate photo of yourself or a friend.
Also, Twitter gives you the option to have your location attached to your tweets -- on mobile devices, it's a small GPS symbol you can tap when you type your tweet — but you might not choose to share this information publicly.
On a related note, it's recommended to avoid third party applications that promise to get you followers, as these usually break Twitter's terms of service -- and might get your account suspended.
More information on followers, including public versus private tweets, is available here.