With certain web browsers (including Mozilla and Internet Explorer) you can access websites and sign up right from the program window. This saves you time since you won't have to open up your web browser, find the website, and log in. Another feature that's interesting but not essential is the automatic password generator. Using this will ensure that your accounts are kept secure. Keep in mind when you use it, though, that it's always smart to keep a copy of your new password on hand.
ScaraBay is a very useful tool for people who have many usernames and passwords for lots of different websites, which nowadays is very common.