Alright, get your mind out of the gutter….were talking about websites. When planning to build your online empire one questions that repeatedly comes up is whether to build one giant website, or create a number of smaller separate sites.
While each site presents its own set of unique circumstances I would advice that in most cases you will want to build one big site. Google seems to favor large sites and I can understand why. Search engines are looking to give users the best experience possible, so if a website has plenty of related content then searchers are probably going to be able to find what they were searching for.
Take advantage of the influence that these sites are given by continuing to build out your content with more articles or blog entries. This should not only help with your top keyword phrases but also with small long tailed terms that can help generate traffic which you wouldn't have normally seen.
What about sub-domains you may ask? Some developers like to break up content this way but I would suggest that this is not the answer. Search engines see sub domains much like they see separate websites. By separating your site into different sub domains you really aren't doing yourself any favors and you won't see the benefit that you can get with one large site.
Remember, just because large sites tend to do better doesn't mean that you should combine your 'pet food' and 'movie review' sites. Search engines can take into account the overall theme and as they continue to get smarter will also get better at differentiating sites that don't provide users a good experience. Also, from a usability perspective having various off-topic sites all bundled together just doesn't make sense.
It's all in the way you move it.
OK, perhaps you have recently built a few small topic related websites and want to consolidate them into one. The best thing to do would be to use a 301 redirect. By using this you will not only be redirecting the website, but you will be redirecting any links that it may have acquired.