You should read:
http://www.wired.com/2012/08/apple-amazon-mat-honan-hacking/
>> It turns out, a billing address and the last four digits of a credit card number are the only two pieces of information anyone needs to get into your iCloud account. Once supplied, Apple will issue a temporary password, and that password grants access to iCloud. <<
[Apple may have changed their policy meanwhile, but likely others did not]
Like don't reveal unnecessary information if you don't have to. It's low effort, high risk.