With how many pages there are on the web, quality will usually win over quantity.
With that being said, sometimes it will make sense to have multiple, similar
websites covering slightly different topics. Doing this can help you create topically
authoritative inbound links to different sites in your network and give you a multibranded
approach to marketing.
However, you want to make sure your sites are all different and unique. If your
sites are extremely similar, then your sites may receive a spam penalty or have the
nepotistic link popularity discounted. Even worse is that if you interlink them all,
then all of your sites could get penalized at the same time.

Those using strong brands and good ideas can usually do well without creating a
topical network. If you create a topical network expressly to deceive search
engines, then you are taking a risk and your sites may get removed from the search
indexes. In addition, some search engine relevancy algorithms, such as Google’s
current algorithm, tend to favor one authoritative domain over using many smaller
similar domains.
Many of the more aggressive techniques are used by people who create crash-and
burn-domain names. They use a site until it gets penalized and then use a new one.
They actually start building up multiple other sites and networks before the first
even gets penalized. If your brand and domain name are important to you, then
make sure you use caution to protect them.
How you wrap/package/sell the content is important. Many blog networks seem
to be able to get away with murder right now because they are called a blog
network. Other publishers that have tried similar network approaches have got
banned for it. Over time, how blogs are treated may change though, and any way
you slice it, you still need to get links from outside your network.
Keep the following in mind when developing a website network: