This topic goes hand-in-hand with the credibility produced by a domain name.
     Rightly or wrongly, there is a perception that sites hosted under their own domain names are more professional than other sites. This idea comes from two facts: all the major, famous sites have their own domain names... and there are a lot of junk sites hosted on free or ISP hosting services.
     Sadly, it really doesn't matter what you or we think about this, as a certain amount of prejudice has already built up against commercial sites without their own domain names.
     So while you CAN be successful with a free site or an ISP-hosted site, you can be MORE successful with your "own" site.
 

A domain name is just like a sign pointing to your site. You can move the underlying site (change web hosting services) and with a very minor technical adjustment (your new hosting service will help you) the domain name will point to your "new" site. This way, you are free to change hosting services to find a better deal, or if the service you are currently receiving is inadequate.
          The important thing is that none of your visitors' bookmarks will need to change, nor will the move break any links to your site! This is impossible without a domain name.
 

Domain names improve your promotion chances as well as potential customers can find you. 
     Domain names which include common keywords can improve a site's ranking in search results returned by major search engines. 
     To be ranked highly in a search engine means that people searching for a store like yours will likely find your web site. 
     You are in competition with MILLIONS of other websites, so purchasing the right domain name is ESSENTIAL. A domain name, thought, is only the beginning of the benefits as far as web promotion is concerned. 
     Many large Directories (sites listing or reviewing other sites) will not accept to list any site that does not have its own domain name. Yahoo! for example has a tendency to "favour" sites with their own domain name.
     There are various reasons for these policies, but for our purposes really doesn't matter WHY the search engines and directories are doing this - the fact is that they ARE! Can you afford that?
     As the Web continues to grow at a breakneck pace, the situation is bound to get worse for sites that do not have their own domain names.
 

Wouldn't rather your customers find you on the internet with a name that reflects the name of your organization, like this? www.yourcompany.com
instead of like this? www.someobscureisp.com/~business/retail/yourcompany
We think you'll agree that the first is much more memorable and looks more professional.
     Even if you are just considering using the Internet and World Wide Web for your business, it's highly recommended that you register your domain name as soon as possible. 
     Once registered, you will own the domain name and no one else in the world will be able to get it. 
     No matter who you end up deciding to host you website, you will be the owner of the Domain Name and only you be able to use it.
 

A domain name also allows you to receive e-mail at a customized e-mail address like this: yourname@yourcompany.com
instead of like this: yourname@someobscureisp.com
When you have your domain name, you can even have multiple email aliases of the form alias@yourcompany.com. 
     This allows you to assign different email aliases to different functions, all of them pointing to your actual email address. 
Hence, for example, for questions related to the products and services that you sell, you can have an email address like sales@yourcompany.com
For comments/suggestions about your web site, you can direct your customers to feedback@yourcompany.com
     Having different email addresses for different functions not only makes it easier for you to filter your email using your email client program, but also gives your customers the impression that yours is a large, established company with whom it is safe to do business.