I have a site with more categories than I care to admit >750. Content in category Alabama with keywords “apple banana carrot” is completely different from content in category Texas with content “apple banana carrot”.
The concern is that search engines have little way to delineate this content and that having the category name in the slug would help.
While using a URL that includes keywords can improve your site’s search visibility, URLs themselves generally do not have a major impact on a page’s ability to rank. So, while it’s worth thinking about, don’t create otherwise unuseful URLs simply to include a keyword in them.
We already send a few strong signals for categories in addition to what’s on the page (and based on the site hierarchy, Google also knows that this support topic is linked to from the meta.discourse.org/c/support).
Like @Falco said, we added the category to page titles, but we do also have appropriate schema.org markup that contains categories in the breadcrumb.
All these signals are strong enough that Google includes the category breadcrumb in search results instead of the full URL:
Considering Google already knows that the example link above is within the howto page hierarchy, I would be surprised if the category in the URL would make any difference.
I forgot to mention that I think your case makes more sense for actual users than SEO. In a large regional forum I imagine there’d be a lot of topics that both
Don’t specifically mention the region in the title
Are generic enough to be relevant for many regions
So a URL in isolation like community.example.com/t/springfield-restaurant-recommendations could really apply to tons of regions in the US… though sharing a link without context is pretty rare… more likely someone would say:
Check out these restaurant recommendations for your trip [to California]: community.example.com/t/springfield-restaurant-recommendations