Blocking Crawling of Parametered URLs in GSC Will Mean PageRank Will be Lost
Google sees links between two canonical URLs and if there is no canonical destination URL then it will be seen as going nowhere and won’t be used. Practically this isn’t an issue as links aren’t usually to a specific parameter variation, so it is unlikely to be driving a lot of the site’s PageRank.
Having Canonical Tags Set For Parameter URLs Helps Google Understand Connections Between Pages
Google tries to figure out the canonical URL for parameter pages that are included in the GSC parameter handling tool, so they may crawl these pages to identify and understand the canonical set up and connection.
Google May Crawl Parameter URLs Set to Crawl: None in the Parameter Handling Tool in GSC
Google may still crawl parameter URLs, even if you set the parameter to crawl: none in GSC. If you want to ensure the URLs never get crawled John recommends using the robots.txt file instead.
Google Will Read the URL String Contained After the Query Parameter
If you are using a ? query parameter, Google will read the remaining URL string and it is not something which blocks crawling or indexing. However, they will drop anything following a # parameter.
The URL Parameter Tool in GSC is Still Effective
Despite not currently being moved over to the new Search Console, the URL parameter tool is still effective to manage parameter crawling.
Replace Unnecessary URL Parameters with Fragment Identifiers
John recommends replacing unnecessary URL parameters with fragment identifiers because anything after the # is usually dropped for indexing, whereas parameter URLs can be indexed separately.
Use gl or hl Parameters in Google Search URLs to See Rankings for Different Countries
You can use gl= or hl= parameters or use the advanced settings in Google to see rankings for different countries and languages. This doesn’t work for local results as there isn’t a parameter for this.
Internally Linked Parameter URLs Might be Indexed Even if Canonical Points to Clean Version
When using parameter URLs for internal linking, it isn’t always guaranteed that the clean version of the URL be indexed if there is a canonical tag to this version. This is because Google has to weigh up which URL should be shown in search.
Don’t Use URLs That Change on the Fly
If URLs change on the fly to include session IDs, for example, this will cause Google to spend more resources on crawling duplicate content. This will also cause confusion around choosing the right canonical page.