Very true, but to give an example of why it isn't good for this site (or maybe I'm over looking something?):

My main page is a general intro to all of the pet products we offer, with emphasis (and meta tags) focusing on clothes, beds, and collars.
Now if I'm creating a page to sell a crate, it doesn't seem like a good thing to have "clothes" or "bed" in the keywords when they are not mentioned in the crate's meta title, description, nor in the page content.