New answers tagged links
Not at all. StackExchange does it. Google doesn't care if you link to sister sites, as long as you're not committing link spam.
They look to me like they are marketing tags which capture a bunch of things about presentation of the product, e.g. Which version of the web page they showed you that 'inspired' you to link the product, the "often bought with" suggestions, etc. Sort of like bucket testing: a company that big is never not bucketing. It's all grist for the data-analysis ...
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