When you look down at the bottom corner of the screen and your Internet connection says X amount per second, this is a direct reference to bandwidth. Many cable connections and cable modems provide 3 GB per second upload speed to the Internet. This is, again, a direct reference to bandwidth. Bandwidth is simply the speed of information traveling back and forth over an Internet connection.
Data transfer is a completely different concept. The data transfer limit of your website has a very significant impact on your business. Basically, the data transfer limit is how much data you are allowed to transfer in a given amount of time. If you can transfer 100 gigs per month, then as soon as your 100 gigs is hit for the month, your customers will find you unavailable and no matter how much advertising you have in place, you will not be able to sell anything or do any type of business due largely to the fact that you have run out of available data transfer.
While bandwidth, or lack of it, will keep customers from loading your site rapidly, the site will be available if they are patient. But the data transfer limit is a different matter altogether. Once you hit that data transfer limit, you will not be able to do business at all.
In the debate between bandwidth and data transfer, it is important to assess the needs of your business and your website head of time and decide what it is that you're going to require from both of these different types of options. In the case of bandwidth, you'll need to be sure that you can provide the speed necessary for customers to reach you and load your site in a reasonable amount of time. Since people will very quickly surf away from your website if it loads slowly, bandwidth is very important. But data transfer is also important, as once you reach the finite point of data transfer, your website simply will not load at all, no matter how patient your customers are.
Making sure that you have a large enough allotment of bandwidth as well as data transfer limit is very important and requires a lot of thought. Setting up your website through your web host a head of time is going to make all the difference in the world and should require that you set forth these very specific standards long before you make the first contract available.
By discussing your needs ahead of time, you can ensure that you don't run out of bandwidth or that your data transfer limit is it reached to rapidly, ensuring that you have a successful launch and that you don't have any difficulties with customers reaching your website.