Subdomains are effectively the same as domains but with another dot, for example if your domain was plasticsurgery.com, a subdomain could be my.plasticsurgery.com or your.plasticsurgery.com. They can lengthen your domain name significantly, and make it more difficult to remember, but the good news is with most of the lower-cost hosting services you can have as many as you want!
But do you really need them? Could using endless subdomains beneficially affect the rankings of your main domain? Subdomains really came about to help large websites organize themselves. If you look closely at a huge site, you may find a subdomain prefix. This is because when building thousands of pages, subdirectory names can get too long or simply start to look very similar that it is hard to differentiate between them easily.
You own as many subdomains of your original domain name as you want, but that doesn’t mean you can replicate your main site across hundreds of subdomains, it will not improve your main site’s ranking or place in the SERPs (Search Engine Results Pages), in fact the search engines will see the duplicate content and probably penalize you for all the replicated subdomains you have created.
If you intend to build out a huge website, subdomains are a very useful organizational tool if you can plan the structure of your site well. For example you could have marketing.yourdomain.com, sales.yourdomain.com, customerservice.yourdomain.com, but for the majority of ordinary internet marketers this is completely unnecessary.
For a large corporation this delineation of departments may be very useful when numerous employees are adding articles and information to a site – there is always a chance that a subdirectory might need to be used by two entirely separate departments and cause a problem. For example you could have sales.mydomain.com/how-to-license-your-product and customerservice.yourdomain.com/how-to-license-your-product – two entirely different articles written by two separate departments.
If you are starting a website for a rapidly growing company, then chances are you have already planned the hierarchy of your domain with a professional company building your site.
The rules of SEO (Search Engine Optimization) still apply equally to domains and subdomains. The search engines will treat each as a separate entity, if your main site has a high PR, it does not mean that your subdomains will have the same page rank, although you can link the main domain to the subdomains manually and vice versa, you will not be penalized for that.
Some time ago web developers saw a loophole within the search engine ranking system and they would deceive the search engines into thinking that a site was much larger than it actually was by using duplicate or only slightly different content and the same keywords within subdomains. The lid was put on that practice a long time ago for obvious reasons. Many sites were taking top ranking for keywords but they were without substance to back up that ranking.
If you have a large niche that will be covering many subjects, let’s say motorcycles, and you wanted to have a separate subdomain for each brand of motorcycle – it may be a good idea to use subdomains for each brand, rather than purchasing dozens of different domain names for each type of motorcycle. It will save you money and you won’t have to go through the laborious process of finding a good domain for each category. You can also link internally to relevant information, making it a lot easier for a visitor, and it’s beneficial to you because that visitor is staying on your site.
So the use of subdomains really boils down to how big you want your site to be, and how many topics it will cover.
Do you use subdomains on your website? How has this helped your business or did you find them unnecessary and cumbersome after a while?