Legitimate interest is the phrasing used by the legislation, which is why companies use it. The wording of the law is pretty lax so a lot of companies put whatever they want in there. I think the intent of the law is to have those cookies be the kind that the website needs to work. For example, they might use that to store which cookies you chose to enable. If you don’t want analytics cookies, the site would make a note of that in those necessary cookies.
Personally, I have my browser set up to clear cookies when I close it, and I have a few sites set up as exceptions.