Notes from the Google Webmaster Hangouts on the 7th of October, 2016.
Parked Domains Lose Authority
If a domain is dropped for a period of time, John is suggesting the authority ranking signals may be lost.
Consolidating Product Variations onto a Single Page Avoids Dilution
You can have a separate page with unique content for product variations, but this can dilute the authority so John generally recommends consolidating them into a stronger single page which contains the variations in the text.
Testimonials and Reviews Can Add Unique Content
Testimonials and user reviews can contribute additional unique content to your page.
Noindex Search Results Pages and Nofollow Search Navigation
You should noindex your own search results pages as they are generally lower quality, but you can disallow them if they are causing a problem with the server load from being crawled. You can nofollow links on the search navigation to prevent crawling but you should probably have followed links on the results pages which can be useful for finding new pages if they are crawled.
Noindex Pages Pass Authority but Might Be Dropped over Time
A noindexed page can still pass link authority through its followed links, but if it remains noindexed for a long time, Google may drop the page and the authority will be lost.
HTML Errors Might Impact User Engagement, Structured Data and Meta Tags
HTML errors don’t directly impact crawling and ranking, but could have an effect on rankings if the page is broken and the user experience is poor, or if the structured data can’t be correctly picked up. If the head section of the page is broken, some of the meta tags might not be seen.
Google Doesn't Care About HTML Versions
The HTML version you use doesn’t matter for Google, so upgrading to HTML5 won’t make any difference.
Google Treats Comments as Primary Page Content
Google doesn’t distinguish between body content and user comments, but they may differentiate other user generated content.
Excessive URL Parameters and Rewrites Can Cause Crawling Problems
Google can have problems crawling your site if your URL structure has an excessive number of URL parameters and rewrites which redirect to a few pages.
Stuffed Keywords May Be Ignored
If you overstuff the same keywords on a page, Google may just ignore most of them.