The following are not required to get a top ranking but rather are ideas that may be
explored further
If your site contains more than one major subject – like baby diapers and garage
door openers, you should consider splitting your site into multiple sites, one site per
subject. This case is largely a nobrainer.
If you have a site that has several related, but distinct groups of products or services,
the case is not so clearcut. You may be better off spending your time expanding the
size of your main site and organizing it better.
Should you decide to create more than one site for your business, keep the following
points in mind:
Don’t copy your main site onto a separate domain and duplicate pages in order
to get more incoming links. Google can detect this and your site may get
penalized (or even dropped from their index).
Use different hosting companies for each site. The reason being is that Google
may consider multiple similar sites on the same server that are crosslinked
together as potential duplicate sites. The important consideration here is to have
each site hosted on a different Class C block.
A Class C block is that number shown in the third position of an IP address. For
example, for 255.137.xxx.255, xxx represents the Class C block. This number
needs to be different for all your websites and the easiest way to guarantee this
is to use separate Web hosting companies for each site.
It is not advised that you create multiple “mini” sites to help increase your traffic or
number of incoming links. This was a popular technique a couple of years ago but
has largely fallen out of favor due to abuse. There are people reportedly that do well
at these but I am skeptical. Many minisites are junk onepage sites with little content
(or with duplicate content) in the hopes of creating lots of links to boost PageRank.
Google will catch on and you will be sorry you did this.
Create multiple sites only if there is a strong, compelling reason to do so.