Do you have to have them with every kit?
No, I suppose not. But I do like them.
Do you use them on every page?
No. I took a glance at my gallery (some of it.) It looks like on each page, there are often about 6 layouts that did use the kit's alpha.
Do you have ones that you use over and over?
No. I've turned into a mostly one-kit-at-a-time scrapper. Like someone else said, it's nice to have what I might want right there in that one folder.