Some users have more than one Google accounts. For example, if you run more than one blogs, quite likely you have separate GMail accounts for different blogs. Sometimes this cause trouble because you need to sign out and sign in to check emails. This is particularly annoying for Chromebook users since by default the account you used to log-in the computer is the account you entered Google.
How to Use Multiple Sign-in?
In fact, some Google services have already supported multiple sign-in, meaning that you can sign-in to more than one account (actually 10 accounts) using the same browser session. The process is easy.