For around 2 weeks there has been data floating around the SEO circles which shows large fluctuations in search rankings for various properties. Many were quick to draw correlations between the words of Google last year saying a new Penguin update was coming and this set of updates. With the updates continuing over the weekend and into this week, it has been clear to a few of us this probably wasn't penguin. Something Gary Illyes of Google confirmed in this tweet.
@AdilAdilrehman core algorithm. Not penguin
— Gary Illyes (@methode) January 18, 2016
Google Update, Jan 2016 is a CORE Update!
Google Core Updates are surprisingly common. However, it's rare unless its a large update or a set of updates for it to cause such a raft of search ranking flux and over such a period of time - this is clearly what has made many SEO experts jump to the wrong conclusion.
The reality, from my point of view, is that until you know for sure what an update is and (more importantly) is not, you shouldn't go jumping around changing everything on your site or that of your clients. Basing your work on an unproven assumption is more likely to cause damage than good.
Generally large updates take time to settle and are often tweaked in quick succession. Until a period has passed from the update & SEO's can study the outcomes (and most probable causes) it is pretty dangerous to make changes to websites.
Of course, those who see rankings drop will immediately begin to assume they have done wrong or that their whole site has an issue - this is rarely the case. The more likely case is that with a few tweaks those sites can not only regain those rankings but can further them and grow from the update. But this is all based on having the data to back up your theory and conclusions - changing a site mid-google update will mean you may never know the true cause of your ranking drop (which may simply be the normal Google flux).
Fianlly, I should point out that from the data I have seen today, this update hasn't completed or is being tweaked.