FTP is the primary method used by website owners to upload content to their servers or distribute large amounts of data. FTP is easy to use and generally efficient at doing its job, but no one would claim that it is completely secure. Generally speaking, files you upload to your website are public anyway, so you might not care if someone intercepts an FTP session’s contents.
When dealing with private information, however, it is a good idea to use a secure transfer method. It is also a better practice in general to use something secure so that your transactions and possibly client and user transactions are not available for the world to see. SFTP is a method of transferring data over an SSH channel.
There are SFTP clients available, and many FTP clients also support SFTP. They may even refer to it as SSH, since SFTP stands for SSH File Transfer Protocol. SFTP does require the user to have an SSH account, and some web hosting providers do not allow them, but if yours does, it is an excellent alternative to FTP.