The reason they did that was so that they could build up data on the effect of each factor independently.  That way, when the bigwigs get into a meeting and discuss alternative designs, they can predict &quot;Ok, this will have $X effect on revenue but will decrease search latency by Y ms, which itself will have +$X effect on revenue.&quot;<p>I was the first engineer on the first visual redesign that tried to change <i>everything</i> about the page [1].  One of our biggest problems was that since we tried to change everything at once, the metrics went haywire, and we couldn&#x27;t know if a change was because we introduced a left-nav (okay, actually we kinda could, because we&#x27;d experimented with a left-nav on its own beforehand) or because we changed the line spacing or because we cleaned up the logo or because we added icons.  There was effectively no way of &quot;debugging&quot; the user; when user behavior varied from expected, we didn&#x27;t know why.<p>I&#x27;ve got plenty of other stories from that era, but they aren&#x27;t really fit for a public forum.  Happy to discuss privately.  (Kinda ironic when the non-Googler says that to the Googler...)<p>[1] <a href="http:&#x2F;&#x2F;googleblog.blogspot.com&#x2F;2010&#x2F;05&#x2F;spring-metamorphosis-googles-new-look.html" rel="nofollow">http:&#x2F;&#x2F;googleblog.blogspot.com&#x2F;2010&#x2F;05&#x2F;spring-metamorphosis-...</a>