Adding a blog to your website is a great way to build loyalty with existing customers. It can also show potential customers that you're about more than just making money.
Writing about events that your restaurant does, any service work you are involved with, and behind-the-scenes information about dishes and staff are all great ways to connect on a more meaningful level with your customers.
Creating a blog can also help you build links to your site since other websites will be much more likely to link to your site if it contains funny, personal, or useful information for visitors than simply a restaurant menu and phone number.