Type-in traffic is one reason to secure domain names that are closely related to your business. Someone might directly type http://www.organicgrocery.com while another may type http://www.organicBocaRatongrocery.com.
Misspellings is another important reason to own various variations of your actual domain name. It may also prove beneficial to own plural variations of your website.
Once you secure all the names you were interested in purchasing, make sure you follow through and redirect the traffic appropriately. Have your web developer establish a 301 redirect from all your new domains to your canonical URL.
Owning multiple domain names will give you an edge, if done right. If you don’t redirect correctly you will sabotage your SEO efforts.