People carry their phone with them everywhere. They can also carry your store with them everywhere. Don't wait for your customers to come in and find you; have your store in front of them as soon as they think of buying.
A whole new market
Customers interstate and overseas are missing out on your products. An online store makes the whole world into your potential customer base.
Not just online
Online stores help sales in brick and mortar stores. When you list all your products online, you can tell customers about them and get them into your store. It also raises your ranking in search engines.