Without it, these informations would have to be kept in the cookies. Cookies are known to be potential security loopholes, and from time to time you will lose them when your network service provider is doing its routine maintenance. This means cookies are very unreliable.
Cookies are limited, too.
On most browsers, you have up to only about 4KB of cookie space to keep information generated from a web site. The total space of Web Space is 30MB per account. Web Space allows remote linking. WSTK is designed with simplicity and ease of use in mind, and it's very robust. AKA passive-FTP mode.