Basically it encrypts the data between the client (browser) and the server (host). No hacker/cracker can break in and tap the connection hand hence will not be able to retrieve any useful information out of the data he/she would have collected. This is very crucial when you are transmittin privacy related information. For example payment details. Eg: - PayPal uses it throughout their website. (http://www.paypal.com) - My webhosting company uses SSL when customers signup (http://client.infinitetech.in). NOTE: Using SSL, your site will load a lot slower and there is more resource needed than using the usual HTTP:80 protocol.