Matt Belkin from Omniture wrote a blog post the other day that gave some great information about using Visitors versus Unique Visitors for traffic analysis. He gave detailed reasons why Visitors is a far better metric, but I’d say the question isn’t an “or” question but an “and” question.
Let me clarify what I mean here. I would use both Unique Visitors AND Visitors in your analysis. To me, they give you different information. Trying to use one or the other is like deciding between snowshoes or sandals. One is for summer, one is for snow, it’s is that simple. The trick with traffic analysis is finding out what season it is.
It is all very simple. If you are an ecommerce site you want to know who is coming back as a repeat visit because that tells you how effective your site and ads are. By examining your conversion, source, repeats, and uniques you can really nail down where the money is coming from. If you are a blogger you want to know how many people visiting your site are repeat visitors. That tells you if people like your blog and are coming back for more. If you had all unique visitors and no repeats, maybe something is wrong.
Now, I realize that this isn’t an exact Science and Matt raises some interesting questions about the accuracy of measuring Unique Visitors. Keep in mind here that very few things are an exact science and just because we can’t measure it to 99.9999% accuracy doesn’t mean we can’t use the information. It’s directional data we are used to in business, and its direction we need. We aren’t sending anybody to Mars with our analytics package after all.