We are frequently asked about purchasing for our clients multiple domain names for their websites. The theory is, for example, if you are a family law attorney practicing in Columbus Ohio, it would help you get your website listed early in searches if you had multiple domain names each containing your specialty areas and locations.
Some people wish to have separate websites and or different domain name for each related area so that the domain name will help get them listed in a search for that area of concentration. This reasoning came into being because Google placed a little too much emphasis on the words in the domain name. There was a time when you could get even a one page site listed for the key words in the domain name. This has not been true for several words. In addition, having several domain names is encouraged by the registrars themselves. They suggest additional names and offer a low ball price for the first year (makes it sound tempting).
Here are some principals that are, all too often, not considered:
Having a domain name that redirects to a website that is under a different domain name does absolutely no good. If you have no information behind the domain name Google will all but ignore it.
The larger website has (usually) more importance. This means that if you have a website describing your carpet cleaning business and have 3 pages, it will generally not be as important (in a Google search) as one with 50 pages. This is providing that the larger site has relevant information about carpet cleaning, carpets, and problems with cleaners and so on.
The more traffic that goes to your website the more important it is as far as Google is concerned. This is one of the Ranking Factors that Google uses. If your site has 200 visitors per month it is not as big a ranking factor as one that has 900.
These factors are not simply additive either. If you have 3 websites, each with 500 visitors per month, collectively they will not be as important as one website that has 1,500 visitors per month. The same way a diamond that is ½ the size of another is worth quite a bit less half the price of the larger stone all things being equal.
Unless you have multiple unrelated businesses or have extremely large following, you are better off having all your content on one website (under multiple pages of course) and under one domain name.