It is text-based, so it's still something an older machine can do well. Messages are left on the mail server, so once you are logged out, no copies of any messages are left on the local machine. Windows style interface. Great capabilities or printing, linking documents, attachments, etc. Can be used on any machine with a web browser.
Messages reside on the mail server.
Usually, printing is a hassle. You can highlight and copy text for use in another program, however. Telnet does not support graphical attachments to your email. It relies on some other program running on the mail server. Stored mail files can usually be accessed by anyone starting the browser program.