Previously: 1. Security
As well as providing important security to your users the presence of an SSL certificate also enhances user confidence in your website and removes some of the fears they might have about giving their data over to you.
Many websites have a section where users can at least log in and perform some tasks such as check messages, manage their personal information, or make a purchase of a service or product.
Without an SSL certificate all this information is open to the public and many more people are becoming aware that their personal security depends on the security of the websites they use.
Users now know to look for the padlock symbol or green address bar. If displayed, the padlock gives peace of mind that their information is being kept secure. It’s a simple and increasingly inexpensive thing but, to your user, that little symbol is a big deal.
If you are asking for users to provide you with their information keeping it private and secure should be your number one priority.