Well first of all most big websites out there these days have hundreds of mini sites or sites that they have established that are relevant and link to their main site. This is good if the sites that are linking in are from different ip addresses as it tells the search engines that they are not necessarily from the same owner.
Others say that buying links would save you the hassle of registering new sites and be just as effective. There are 2 sides to the coin. The 1st thing is when buying links it does not ensure you a permanent 1 way link. It might be good for some time, but at the end of the day you are not benefiting from it long term. Sure it can help getting a link from a site that has high page rank that you are looking for, but too much of link buying can also send off alarm bells to Google.
It is not against Googles terms to buy links but it is to sell links based on page rank, and it is against Googles terms to buy links specifically to gain page rank. So nevertheless, I encourage you to believe it is beneficial to do both. Although link buying can be time consuming and expensive to find the sites you want links on, so can building sites, but long term this is the key.
When you buy or develop a site to link to your main site, there are certainly other factors to consider such as the age of the domain you have bought or registered, the relevancy of the domain or site, is it being updated frequently, does the site have backlinks or page rank as well and does it have alot of cached and index pages.
Many site owners think they can just build 100 sites and link to their main site and think they can gain loads of traffic. Wrong, the problem is they don’t realise is it is those sites itself that need to also have alot of backlinks and page rank.
This tells Google that the sites that are linking into the main site have some authority.
So the big question is what works best for you, and do you consider buying sites or buying links to be more effective?