Use both parent and child category for posts?

Replies: 0

Simple SEO question here:

I’m wondering if it makes any difference to search engine crawlers if I select the parent and child category for a post. It seems that if I just select the child category, it still appears in the listing of posts underneath the parent category. I’m okay with this. The only difference it seems to make for UX is that the post itself will either show “child/parent” or just “child” in the category meta.

I guess all I’m really wondering is if one or the either is more SEO-friendly.

Thanks!