In most cases, I think it makes no sense to use multiple analytics packages. For one, the tracking codes can interfere with each other. For another, those calls to outside servers can unnecessarily increase the page load time.

What reasons could I see for using multiple analytics packages? One reason would be to gain additional features and functionality that the combination would give you, i.e. the sum was bigger than its parts. However, I can’t see many cases for this.

The other reason would be to diagnose tracking issues, which you may have eluded to. i.e. the tracking code was stripped from several pages and you only notice that as a result of viewing an abnormal difference in trend lines between the two apps. However, there are other ways to diagnose these kinds of issues without needing multiple apps. One way would be to setup custom alerts using the new Intelligence feature in Google Analytics to look for abnormal variances in pageviews, visitors, etc.

Your second reason talks about accessing the multitude of free tools that Google provides. The analysis tools you mentioned for keyword research, search trends, etc. don’t require an Analytics account. In fact, they don’t even require a Google account at all so I’m not sure of the benefit there.

In short, I disagree. Happy New Year to everyone at PV!