Typically there's an increased scrutiny of web stats immediately after a website relaunch or major updates. Which is not surprising but, unfortunately, probably the worst time for this focus as there's nearly always a blip in performance immediately after major changes.
Even if you've done your homework and tested the new designs with users and you're 100% (well, maybe 99%) sure they will give better results - there's likely to be a bit of downturn for a few days or a week as users get used to the new designs.
A new design might not affect someone coming to your website for the very first time - but a new customer might make a few visits to your site before making a first purchase. So there's a potential for a large number of return visitors to be slightly thrown when they return to a site and find significant changes.
The responses can mirror the Kübler-Ross model of dealing with grief. Your users will go through 5 stages:
- Denial - we generally don't like change and would have preferred to stick with what was familiar and the faults we have learnt to deal with
- Anger - a negative emotional response to the change
- Bargaining - trying to find a compromise, perhaps trying to make the new system work like the old one
- Depression - remembering how much you used to like this website
- Acceptance - realisation that the changes actually are improvements
In part it's an argument for continual iterative changes so users are rarely surprised with major changes. But in reality this isn't always possible. Essentially it is human nature and unavoidable. If you have done thorough usability testing and are confident in the new designs, then the downturn should only be short-lived. Just be aware of it and don't panic if orders drop off the day after a major relaunch.
The caveat here is: even with your good research and testing phases and confidence that you have delivered good solutions - don't be complacent and believe that they're perfect.
Once you see orders return to normal levels and hopefully begin to exceed them - it is time to look at further refinements. It's extremely unlikely everything will be 100% optimised on launch so once users have become familiar with a major design change, it's the best time to start refining. And at this point the changes can be small and unlikely to cause any significant reactions from users in the way the main relaunch did.