How does using a nickname help protect my account and reduce spam?
Spammers may be able to figure out your email address by looking at your Yahoo! ID, which is often the same as the first part of your email address. With a nickname, you don't reveal your email address or Yahoo! ID. This helps to protect your account and reduce spam.
Using a nickname also gives you a consistent identity across all of Yahoo!, making it easier for you to participate, share, and gain recognition across multiple Yahoo! sites.
Unless you choose to display your Yahoo! ID or post content as "A Yahoo! Contributor," your nickname displays wherever your Yahoo! identity appears.