My goal is to explain how the refresh will update your business' website in the simplest way possible.
Google Panda 4.2 is a refresh to the algorithm, or how Google is ranking websites in search results. Panda's focus is quality. Showing lower quality or "thin" websites less, while higher quality sites will be ranked higher.
It certainly can impact your website traffic dramatically either positively or negatively...or it might not impact you at all. Overall this refresh will affect 2-3% of all search queries and is rolled out over an extended period of time, not instantly.
If your website traffic is impacted, you may already see that reflected in your Google Analytics, but keep an eye out for the next few weeks to be sure.
As previously mentioned, Panda focuses on quality. Think user experience here.
Remember, think user experience. Google is getting smarter and can tell (somewhat) if a user will have a good experience or not. You should know what type of user experience your website provides.
If you saw a positive impact in your website traffic, great! Just see the list above and double check those items don't apply to you. Just because you weren't impacted this time it doesn't mean you won't be impacted next time.
Unfortunately you can't just tell Google you fixed them and expect to regain visibility and traffic. You'll have to wait for the next Panda refresh which could be next week, next month, next year...nobody knows.
Yes. You'll obviously care more if you website traffic drops significantly. If you don't have a clue about your website metrics, take notice. You may be impacted by the refresh and not even know it.