I know some people who save butter papers for greasing cookie sheets, etc, and that's fine. I do not. I use a scraper (the flexible, silicone type) and I scrape down the paper to get every bit of butter off and then the wax paper is generally butter free and has no use for greasing. This is especially helpful when you let your butter soften in the wax and lots of it likes to stick. You can lose 1-2 teaspoons that way easy!
So scrape it off, or grease stuff with it - but don't let all of that wonderful (and $3 per pound) butter get wasted!