One of the most interesting articles I read a while ago discussed how a website owner liked to use two analytic programs on their site. The two discussed was Google Analytics and Pikwik.
The reasoning was really simple – analytic programs have a tendency to update and change the way they track data without informing you. As such, it’s often useful to keep track of the data using 2 different programs so that a drastic change can be tracked backwards based on previous data. Or put another way – you can tell if it’s your site or just the software.
There’s another subtler reason buried there too of course – Analytic programs track the same information differently. It can often be useful to have 2 programs track your data separately if you understand how the programs track / categorise that information extract more knowledge.
Sometimes, the reasoning can be even easier – sometimes, one software just presents the data better. I definitely enjoy the presentation by Pikwik where it automatically tracks sales by categories for us, something Google Analytics doesn’t do without a lot more work.