This should not have been marked as the correct answer.@mrmucca's question is not related to the Adobe Fonts service (formerly Typekit) at all.
If you place fonts into this folder (there's a Windows equivalent, too), they will become instantly available in Adobe applications, which saves you from installing them system-wide, and eliminates issues with font caching. This is handy for type designers or anyone who works with fonts that are frequently updated. It's a very old feature that isn't well-documented anymore on Adobe's website, far as I can tell.
I've been looking for an answer to this as well, and as far as I can tell, Adobe XD does not load fonts from these folders the way that Illustrator, InDesign and Photoshop do.