I don’t even care. I just put them in anyway. Just to cover all my bases. Product listings, blogs, webpages, I try everything possible to get my websites and pages listed high no matter what Google or whoever says something matters or not. I edit my product listings in a spreadsheet so I just copy/paste the search keywords column into the meta keywords column, takes half a second.

With long tail keywords, you're able to be more targeted.

Take the term 'toxic relationship' for example, this is quite a broad term. Somebody searching for this may be looking for info on what a toxic relationship is, wondering if they're in a toxic relationship themself,or a whole range of other possibilities.

However, targeting what we'd call long tail keywords, such as 'ending a toxic relationship', 'how to end a toxic relationship', etc, means that you will have a much better chance of ranking for keywords that align your content perfectly with the search intent of the end user.

In terms of what these longtail keywords should be, that's where keyword research is essential. Using a tool like SEMRush's Keyword Magic Tool, or Ubersuggest will let you explore similar keywords and identify the ones that have significant search volume.

One final point, because Yoast only tracks one focus keyword, newer users think they only need to optimise for one focus keyword (i fell into the same trap when I was fist learning). My advice would be to decide on one primary keyword, and expand upon this with several secondary keywords. This will broaden the organic visibility of your content and ensure that it appears for multiple relevant search terms.

Hope this helps, good luck!